-@node Users and Groups
+@node Users and Groups, System Management, Name Service Switch, Top
+@c %MENU% How users are identified and classified
@chapter Users and Groups
Every user who can log in on the system is identified by a unique number
* Who Logged In:: Getting the name of the user who logged in,
or of the real user ID of the current process.
+* User Accounting Database:: Keeping information about users and various
+ actions in databases.
+
* User Database:: Functions and data structures for
accessing the user database.
* Group Database:: Functions and data structures for
accessing the group database.
-* Netgroup Database:: Functions for accessing the netgroup database.
-* Database Example:: Example program showing use of database
+* Database Example:: Example program showing the use of database
inquiry functions.
+* Netgroup Database:: Functions for accessing the netgroup database.
@end menu
-@node User and Group IDs, Process Persona, Users and Groups, Users and Groups
+@node User and Group IDs
@section User and Group IDs
@cindex login name
@cindex group name
@cindex group ID
-Users are classified in @dfn{groups}. Each user name also belongs to
-one or more groups, and has one @dfn{default group}. Users who are
-members of the same group can share resources (such as files) that are
-not accessible to users who are not a member of that group. Each group
-has a @dfn{group name} and @dfn{group ID}. @xref{Group Database},
-for how to find information about a group ID or group name.
-
-@node Process Persona, Why Change Persona, User and Group IDs, Users and Groups
+Users are classified in @dfn{groups}. Each user name belongs to one
+@dfn{default group} and may also belong to any number of
+@dfn{supplementary groups}. Users who are members of the same group can
+share resources (such as files) that are not accessible to users who are
+not a member of that group. Each group has a @dfn{group name} and
+@dfn{group ID}. @xref{Group Database}, for how to find information
+about a group ID or group name.
+
+@node Process Persona
@section The Persona of a Process
@cindex persona
@cindex effective user ID
@cindex effective group ID
+@cindex supplementary group IDs
-@c !!! bogus; not single ID. set of effective group IDs (and, in GNU,
-@c set of effective UIDs) determines privilege. lying here and then
-@c telling the truth below is confusing.
-At any time, each process has a single user ID and a group ID which
-determine the privileges of the process. These are collectively called
-the @dfn{persona} of the process, because they determine ``who it is''
-for purposes of access control. These IDs are also called the
-@dfn{effective user ID} and @dfn{effective group ID} of the process.
+@c When Hurd is more widely used, explain multiple effective user IDs
+@c here. -zw
+At any time, each process has an @dfn{effective user ID}, a @dfn{effective
+group ID}, and a set of @dfn{supplementary group IDs}. These IDs
+determine the privileges of the process. They are collectively
+called the @dfn{persona} of the process, because they determine ``who it
+is'' for purposes of access control.
Your login shell starts out with a persona which consists of your user
-ID and your default group ID.
-@c !!! also supplementary group IDs.
-In normal circumstances, all your other processes inherit these values.
+ID, your default group ID, and your supplementary group IDs (if you are
+in more than one group). In normal circumstances, all your other processes
+inherit these values.
@cindex real user ID
@cindex real group ID
Both the real and effective user ID can be changed during the lifetime
of a process. @xref{Why Change Persona}.
-@cindex supplementary group IDs
-In addition, a user can belong to multiple groups, so the persona
-includes @dfn{supplementary group IDs} that also contribute to access
-permission.
-
-For details on how a process's effective user IDs and group IDs affect
+For details on how a process's effective user ID and group IDs affect
its permission to access files, see @ref{Access Permission}.
-The user ID of a process also controls permissions for sending signals
-using the @code{kill} function. @xref{Signaling Another Process}.
+The effective user ID of a process also controls permissions for sending
+signals using the @code{kill} function. @xref{Signaling Another
+Process}.
-@node Why Change Persona, How Change Persona, Process Persona, Users and Groups
+Finally, there are many operations which can only be performed by a
+process whose effective user ID is zero. A process with this user ID is
+a @dfn{privileged process}. Commonly the user name @code{root} is
+associated with user ID 0, but there may be other user names with this
+ID.
+@c !!! should mention POSIX capabilities here.
+
+@node Why Change Persona
@section Why Change the Persona of a Process?
The most obvious situation where it is necessary for a process to change
user ID to be that for @code{games}. In effect, the program must
adopt the persona of @code{games} so it can write the scores file.
-@node How Change Persona, Reading Persona, Why Change Persona, Users and Groups
+@node How Change Persona
@section How an Application Can Change Persona
@cindex @code{setuid} programs
+@cindex saved set-user-ID
+@cindex saved set-group-ID
+@cindex @code{_POSIX_SAVED_IDS}
The ability to change the persona of a process can be a source of
unintentional privacy violations, or even intentional abuse. Because of
change to a particular user or group. This is the function of the setuid
and setgid bits of a file's access mode. @xref{Permission Bits}.
-When the setuid bit of an executable file is set, executing that file
-automatically changes the effective user ID to the user that owns the
-file. Likewise, executing a file whose setgid bit is set changes the
-effective group ID to the group of the file. @xref{Executing a File}.
-Creating a file that changes to a particular user or group ID thus
-requires full access to that user or group ID.
+When the setuid bit of an executable file is on, executing that file
+gives the process a third user ID: the @dfn{file user ID}. This ID is
+set to the owner ID of the file. The system then changes the effective
+user ID to the file user ID. The real user ID remains as it was.
+Likewise, if the setgid bit is on, the process is given a @dfn{file
+group ID} equal to the group ID of the file, and its effective group ID
+is changed to the file group ID.
+
+If a process has a file ID (user or group), then it can at any time
+change its effective ID to its real ID and back to its file ID.
+Programs use this feature to relinquish their special privileges except
+when they actually need them. This makes it less likely that they can
+be tricked into doing something inappropriate with their privileges.
+
+@strong{Portability Note:} Older systems do not have file IDs.
+To determine if a system has this feature, you can test the compiler
+define @code{_POSIX_SAVED_IDS}. (In the POSIX standard, file IDs are
+known as saved IDs.)
@xref{File Attributes}, for a more general discussion of file modes and
accessibility.
-A process can always change its effective user (or group) ID back to its
-real ID. Programs do this so as to turn off their special privileges
-when they are not needed, which makes for more robustness.
-
-@c !!! talk about _POSIX_SAVED_IDS
-
-@node Reading Persona, Setting User ID, How Change Persona, Users and Groups
+@node Reading Persona
@section Reading the Persona of a Process
Here are detailed descriptions of the functions for reading the user and
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} uid_t
-This is an integer data type used to represent user IDs. In the GNU
-library, this is an alias for @code{unsigned int}.
+This is an integer data type used to represent user IDs. In
+@theglibc{}, this is an alias for @code{unsigned int}.
@end deftp
@comment sys/types.h
@comment POSIX.1
@deftp {Data Type} gid_t
-This is an integer data type used to represent group IDs. In the GNU
-library, this is an alias for @code{unsigned int}.
+This is an integer data type used to represent group IDs. In
+@theglibc{}, this is an alias for @code{unsigned int}.
@end deftp
@comment unistd.h
@end smallexample
@end deftypefun
-@node Setting User ID, Setting Groups, Reading Persona, Users and Groups
+@node Setting User ID
@section Setting the User ID
This section describes the functions for altering the user ID (real
@comment unistd.h
@comment POSIX.1
-@deftypefun int setuid (uid_t @var{newuid})
-This function sets both the real and effective user ID of the process
-to @var{newuid}, provided that the process has appropriate privileges.
-@c !!! also sets saved-id
-
-If the process is not privileged, then @var{newuid} must either be equal
-to the real user ID or the saved user ID (if the system supports the
-@code{_POSIX_SAVED_IDS} feature). In this case, @code{setuid} sets only
-the effective user ID and not the real user ID.
-@c !!! xref to discussion of _POSIX_SAVED_IDS
-
-The @code{setuid} function returns a value of @code{0} to indicate
+@deftypefun int seteuid (uid_t @var{neweuid})
+This function sets the effective user ID of a process to @var{neweuid},
+provided that the process is allowed to change its effective user ID. A
+privileged process (effective user ID zero) can change its effective
+user ID to any legal value. An unprivileged process with a file user ID
+can change its effective user ID to its real user ID or to its file user
+ID. Otherwise, a process may not change its effective user ID at all.
+
+The @code{seteuid} function returns a value of @code{0} to indicate
successful completion, and a value of @code{-1} to indicate an error.
The following @code{errno} error conditions are defined for this
function:
@table @code
@item EINVAL
-The value of the @var{newuid} argument is invalid.
+The value of the @var{neweuid} argument is invalid.
@item EPERM
-The process does not have the appropriate privileges; you do not
-have permission to change to the specified ID.
+The process may not change to the specified ID.
@end table
+
+Older systems (those without the @code{_POSIX_SAVED_IDS} feature) do not
+have this function.
+@end deftypefun
+
+@comment unistd.h
+@comment POSIX.1
+@deftypefun int setuid (uid_t @var{newuid})
+If the calling process is privileged, this function sets both the real
+and effective user ID of the process to @var{newuid}. It also deletes
+the file user ID of the process, if any. @var{newuid} may be any
+legal value. (Once this has been done, there is no way to recover the
+old effective user ID.)
+
+If the process is not privileged, and the system supports the
+@code{_POSIX_SAVED_IDS} feature, then this function behaves like
+@code{seteuid}.
+
+The return values and error conditions are the same as for @code{seteuid}.
@end deftypefun
@comment unistd.h
means not to change the effective user ID.
The @code{setreuid} function exists for compatibility with 4.3 BSD Unix,
-which does not support saved IDs. You can use this function to swap the
+which does not support file IDs. You can use this function to swap the
effective and real user IDs of the process. (Privileged processes are
-not limited to this particular usage.) If saved IDs are supported, you
+not limited to this particular usage.) If file IDs are supported, you
should use that feature instead of this function. @xref{Enable/Disable
Setuid}.
@end table
@end deftypefun
-@node Setting Groups, Enable/Disable Setuid, Setting User ID, Users and Groups
+@node Setting Groups
@section Setting the Group IDs
This section describes the functions for altering the group IDs (real
@pindex unistd.h
@pindex sys/types.h
+@comment unistd.h
+@comment POSIX.1
+@deftypefun int setegid (gid_t @var{newgid})
+This function sets the effective group ID of the process to
+@var{newgid}, provided that the process is allowed to change its group
+ID. Just as with @code{seteuid}, if the process is privileged it may
+change its effective group ID to any value; if it isn't, but it has a
+file group ID, then it may change to its real group ID or file group ID;
+otherwise it may not change its effective group ID.
+
+Note that a process is only privileged if its effective @emph{user} ID
+is zero. The effective group ID only affects access permissions.
+
+The return values and error conditions for @code{setegid} are the same
+as those for @code{seteuid}.
+
+This function is only present if @code{_POSIX_SAVED_IDS} is defined.
+@end deftypefun
+
@comment unistd.h
@comment POSIX.1
@deftypefun int setgid (gid_t @var{newgid})
This function sets both the real and effective group ID of the process
-to @var{newgid}, provided that the process has appropriate privileges.
-@c !!! also sets saved-id
+to @var{newgid}, provided that the process is privileged. It also
+deletes the file group ID, if any.
-If the process is not privileged, then @var{newgid} must either be equal
-to the real group ID or the saved group ID. In this case, @code{setgid}
-sets only the effective group ID and not the real group ID.
+If the process is not privileged, then @code{setgid} behaves like
+@code{setegid}.
The return values and error conditions for @code{setgid} are the same
-as those for @code{setuid}.
+as those for @code{seteuid}.
@end deftypefun
@comment unistd.h
@comment BSD
-@deftypefun int setregid (gid_t @var{rgid}, fid_t @var{egid})
+@deftypefun int setregid (gid_t @var{rgid}, gid_t @var{egid})
This function sets the real group ID of the process to @var{rgid} and
the effective group ID to @var{egid}. If @var{rgid} is @code{-1}, it
means not to change the real group ID; likewise if @var{egid} is
@code{-1}, it means not to change the effective group ID.
The @code{setregid} function is provided for compatibility with 4.3 BSD
-Unix, which does not support saved IDs. You can use this function to
+Unix, which does not support file IDs. You can use this function to
swap the effective and real group IDs of the process. (Privileged
-processes are not limited to this usage.) If saved IDs are supported,
+processes are not limited to this usage.) If file IDs are supported,
you should use that feature instead of using this function.
@xref{Enable/Disable Setuid}.
as those for @code{setreuid}.
@end deftypefun
-The GNU system also lets privileged processes change their supplementary
+@code{setuid} and @code{setgid} behave differently depending on whether
+the effective user ID at the time is zero. If it is not zero, they
+behave like @code{seteuid} and @code{setegid}. If it is, they change
+both effective and real IDs and delete the file ID. To avoid confusion,
+we recommend you always use @code{seteuid} and @code{setegid} except
+when you know the effective user ID is zero and your intent is to change
+the persona permanently. This case is rare---most of the programs that
+need it, such as @code{login} and @code{su}, have already been written.
+
+Note that if your program is setuid to some user other than @code{root},
+there is no way to drop privileges permanently.
+
+The system also lets privileged processes change their supplementary
group IDs. To use @code{setgroups} or @code{initgroups}, your programs
should include the header file @file{grp.h}.
@pindex grp.h
@comment grp.h
@comment BSD
-@deftypefun int setgroups (size_t @var{count}, gid_t *@var{groups})
+@deftypefun int setgroups (size_t @var{count}, const gid_t *@var{groups})
This function sets the process's supplementary group IDs. It can only
be called from privileged processes. The @var{count} argument specifies
the number of group IDs in the array @var{groups}.
@comment grp.h
@comment BSD
-@deftypefun int initgroups (const char *@var{user}, gid_t @var{gid})
-The @code{initgroups} function effectively calls @code{setgroups} to
-set the process's supplementary group IDs to be the normal default for
-the user name @var{user}. The group ID @var{gid} is also included.
-@c !!! explain that this works by reading the group file looking for
-@c groups USER is a member of.
+@deftypefun int initgroups (const char *@var{user}, gid_t @var{group})
+The @code{initgroups} function sets the process's supplementary group
+IDs to be the normal default for the user name @var{user}. The group
+@var{group} is automatically included.
+
+This function works by scanning the group database for all the groups
+@var{user} belongs to. It then calls @code{setgroups} with the list it
+has constructed.
+
+The return values and error conditions are the same as for
+@code{setgroups}.
+@end deftypefun
+
+If you are interested in the groups a particular user belongs to, but do
+not want to change the process's supplementary group IDs, you can use
+@code{getgrouplist}. To use @code{getgrouplist}, your programs should
+include the header file @file{grp.h}.
+@pindex grp.h
+
+@comment grp.h
+@comment BSD
+@deftypefun int getgrouplist (const char *@var{user}, gid_t @var{group}, gid_t *@var{groups}, int *@var{ngroups})
+The @code{getgrouplist} function scans the group database for all the
+groups @var{user} belongs to. Up to *@var{ngroups} group IDs
+corresponding to these groups are stored in the array @var{groups}; the
+return value from the function is the number of group IDs actually
+stored. If *@var{ngroups} is smaller than the total number of groups
+found, then @code{getgrouplist} returns a value of @code{-1} and stores
+the actual number of groups in *@var{ngroups}. The group @var{group} is
+automatically included in the list of groups returned by
+@code{getgrouplist}.
+
+Here's how to use @code{getgrouplist} to read all supplementary groups
+for @var{user}:
+
+@smallexample
+@group
+gid_t *
+supplementary_groups (char *user)
+@{
+ int ngroups = 16;
+ gid_t *groups
+ = (gid_t *) xmalloc (ngroups * sizeof (gid_t));
+ struct passwd *pw = getpwnam (user);
+
+ if (pw == NULL)
+ return NULL;
+
+ if (getgrouplist (pw->pw_name, pw->pw_gid, groups, &ngroups) < 0)
+ @{
+ groups = xrealloc (ngroups * sizeof (gid_t));
+ getgrouplist (pw->pw_name, pw->pw_gid, groups, &ngroups);
+ @}
+ return groups;
+@}
+@end group
+@end smallexample
@end deftypefun
-@node Enable/Disable Setuid, Setuid Program Example, Setting Groups, Users and Groups
+@node Enable/Disable Setuid
@section Enabling and Disabling Setuid Access
A typical setuid program does not need its special access all of the
time. It's a good idea to turn off this access when it isn't needed,
so it can't possibly give unintended access.
-If the system supports the saved user ID feature, you can accomplish
-this with @code{setuid}. When the game program starts, its real user ID
-is @code{jdoe}, its effective user ID is @code{games}, and its saved
-user ID is also @code{games}. The program should record both user ID
-values once at the beginning, like this:
+If the system supports the @code{_POSIX_SAVED_IDS} feature, you can
+accomplish this with @code{seteuid}. When the game program starts, its
+real user ID is @code{jdoe}, its effective user ID is @code{games}, and
+its saved user ID is also @code{games}. The program should record both
+user ID values once at the beginning, like this:
@smallexample
user_user_id = getuid ();
Then it can turn off game file access with
@smallexample
-setuid (user_user_id);
+seteuid (user_user_id);
@end smallexample
@noindent
and turn it on with
@smallexample
-setuid (game_user_id);
+seteuid (game_user_id);
@end smallexample
@noindent
Throughout this process, the real user ID remains @code{jdoe} and the
-saved user ID remains @code{games}, so the program can always set its
+file user ID remains @code{games}, so the program can always set its
effective user ID to either one.
-On other systems that don't support the saved user ID feature, you can
+On other systems that don't support file user IDs, you can
turn setuid access on and off by using @code{setreuid} to swap the real
and effective user IDs of the process, as follows:
@smallexample
#ifdef _POSIX_SAVED_IDS
- setuid (user_user_id);
+ seteuid (user_user_id);
#else
setreuid (geteuid (), getuid ());
#endif
@end smallexample
-@node Setuid Program Example, Tips for Setuid, Enable/Disable Setuid, Users and Groups
+@node Setuid Program Example
@section Setuid Program Example
Here's an example showing how to set up a program that changes its
effective user ID.
-This is part of a game program called @code{caber-toss} that
-manipulates a file @file{scores} that should be writable only by the game
-program itself. The program assumes that its executable
-file will be installed with the set-user-ID bit set and owned by the
-same user as the @file{scores} file. Typically, a system
-administrator will set up an account like @code{games} for this purpose.
+This is part of a game program called @code{caber-toss} that manipulates
+a file @file{scores} that should be writable only by the game program
+itself. The program assumes that its executable file will be installed
+with the setuid bit set and owned by the same user as the @file{scores}
+file. Typically, a system administrator will set up an account like
+@code{games} for this purpose.
The executable file is given mode @code{4755}, so that doing an
@samp{ls -l} on it produces output like:
@end smallexample
@noindent
-The set-user-ID bit shows up in the file modes as the @samp{s}.
+The setuid bit shows up in the file modes as the @samp{s}.
The scores file is given mode @code{644}, and doing an @samp{ls -l} on
it shows:
Here are the parts of the program that show how to set up the changed
user ID. This program is conditionalized so that it makes use of the
-saved IDs feature if it is supported, and otherwise uses @code{setreuid}
+file IDs feature if it is supported, and otherwise uses @code{setreuid}
to swap the effective and real user IDs.
@smallexample
#include <stdlib.h>
-/* @r{Save the effective and real UIDs.} */
+/* @r{Remember the effective and real UIDs.} */
static uid_t euid, ruid;
int status;
#ifdef _POSIX_SAVED_IDS
- status = setuid (euid);
+ status = seteuid (euid);
#else
status = setreuid (ruid, euid);
#endif
int status;
#ifdef _POSIX_SAVED_IDS
- status = setuid (ruid);
+ status = seteuid (ruid);
#else
status = setreuid (euid, ruid);
#endif
int
main (void)
@{
- /* @r{Save the real and effective user IDs.} */
+ /* @r{Remember the real and effective user IDs.} */
ruid = getuid ();
euid = geteuid ();
undo_setuid ();
effective user ID back to the real user ID. This is so that any other
file accesses that are performed while the user is playing the game use
the real user ID for determining permissions. Only when the program
-needs to open the scores file does it switch back to the original
-effective user ID, like this:
+needs to open the scores file does it switch back to the file user ID,
+like this:
@smallexample
/* @r{Record the score.} */
@end group
@end smallexample
-@node Tips for Setuid, Who Logged In, Setuid Program Example, Users and Groups
+@node Tips for Setuid
@section Tips for Writing Setuid Programs
It is easy for setuid programs to give the user access that isn't
@code{root} unless it is absolutely necessary. If the resource is
specific to your particular program, it's better to define a new,
nonprivileged user ID or group ID just to manage that resource.
+It's better if you can write your program to use a special group than a
+special user.
@item
-Be cautious about using the @code{system} and @code{exec} functions in
-combination with changing the effective user ID. Don't let users of
-your program execute arbitrary programs under a changed user ID.
-Executing a shell is especially bad news. Less obviously, the
-@code{execlp} and @code{execvp} functions are a potential risk (since
-the program they execute depends on the user's @code{PATH} environment
-variable).
+Be cautious about using the @code{exec} functions in combination with
+changing the effective user ID. Don't let users of your program execute
+arbitrary programs under a changed user ID. Executing a shell is
+especially bad news. Less obviously, the @code{execlp} and @code{execvp}
+functions are a potential risk (since the program they execute depends
+on the user's @code{PATH} environment variable).
If you must @code{exec} another program under a changed ID, specify an
absolute file name (@pxref{File Name Resolution}) for the executable,
containing directories are such that ordinary users cannot replace it
with some other program.
+You should also check the arguments passed to the program to make sure
+they do not have unexpected effects. Likewise, you should examine the
+environment variables. Decide which arguments and variables are safe,
+and reject all others.
+
+You should never use @code{system} in a privileged program, because it
+invokes a shell.
+
@item
Only use the user ID controlling the resource in the part of the program
that actually uses that resource. When you're finished with it, restore
uses the real user and group IDs, rather than the effective IDs.
@end itemize
-@node Who Logged In, User Database, Tips for Setuid, Users and Groups
+@node Who Logged In
@section Identifying Who Logged In
@cindex login name, determining
@cindex user ID, determining
You can use the functions listed in this section to determine the login
name of the user who is running a process, and the name of the user who
logged in the current session. See also the function @code{getuid} and
-friends (@pxref{Reading Persona}).
+friends (@pxref{Reading Persona}). How this information is collected by
+the system and how to control/add/remove information from the background
+storage is described in @ref{User Accounting Database}.
The @code{getlogin} function is declared in @file{unistd.h}, while
@code{cuserid} and @code{L_cuserid} are declared in @file{stdio.h}.
subsequent calls to this function or to @code{getlogin}.
The use of this function is deprecated since it is marked to be
-withdrawn in XPG4.2 and it is already removed in POSIX.1.
+withdrawn in XPG4.2 and has already been removed from newer revisions of
+POSIX.1.
@end deftypefun
@comment stdio.h
These functions let your program identify positively the user who is
running or the user who logged in this session. (These can differ when
-setuid programs are involved; @xref{Process Persona}.) The user cannot
+setuid programs are involved; see @ref{Process Persona}.) The user cannot
do anything to fool these functions.
For most purposes, it is more useful to use the environment variable
precisely because the user can set @code{LOGNAME} arbitrarily.
@xref{Standard Environment}.
-@node User Database, Group Database, Who Logged In, Users and Groups
+
+@node User Accounting Database
+@section The User Accounting Database
+@cindex user accounting database
+
+Most Unix-like operating systems keep track of logged in users by
+maintaining a user accounting database. This user accounting database
+stores for each terminal, who has logged on, at what time, the process
+ID of the user's login shell, etc., etc., but also stores information
+about the run level of the system, the time of the last system reboot,
+and possibly more.
+
+The user accounting database typically lives in @file{/etc/utmp},
+@file{/var/adm/utmp} or @file{/var/run/utmp}. However, these files
+should @strong{never} be accessed directly. For reading information
+from and writing information to the user accounting database, the
+functions described in this section should be used.
+
+
+@menu
+* Manipulating the Database:: Scanning and modifying the user
+ accounting database.
+* XPG Functions:: A standardized way for doing the same thing.
+* Logging In and Out:: Functions from BSD that modify the user
+ accounting database.
+@end menu
+
+@node Manipulating the Database
+@subsection Manipulating the User Accounting Database
+
+These functions and the corresponding data structures are declared in
+the header file @file{utmp.h}.
+@pindex utmp.h
+
+@comment utmp.h
+@comment SVID
+@deftp {Data Type} {struct exit_status}
+The @code{exit_status} data structure is used to hold information about
+the exit status of processes marked as @code{DEAD_PROCESS} in the user
+accounting database.
+
+@table @code
+@item short int e_termination
+The exit status of the process.
+
+@item short int e_exit
+The exit status of the process.
+@end table
+@end deftp
+
+@deftp {Data Type} {struct utmp}
+The @code{utmp} data structure is used to hold information about entries
+in the user accounting database. On @gnusystems{} it has the following
+members:
+
+@table @code
+@item short int ut_type
+Specifies the type of login; one of @code{EMPTY}, @code{RUN_LVL},
+@code{BOOT_TIME}, @code{OLD_TIME}, @code{NEW_TIME}, @code{INIT_PROCESS},
+@code{LOGIN_PROCESS}, @code{USER_PROCESS}, @code{DEAD_PROCESS} or
+@code{ACCOUNTING}.
+
+@item pid_t ut_pid
+The process ID number of the login process.
+
+@item char ut_line[]
+The device name of the tty (without @file{/dev/}).
+
+@item char ut_id[]
+The inittab ID of the process.
+
+@item char ut_user[]
+The user's login name.
+
+@item char ut_host[]
+The name of the host from which the user logged in.
+
+@item struct exit_status ut_exit
+The exit status of a process marked as @code{DEAD_PROCESS}.
+
+@item long ut_session
+The Session ID, used for windowing.
+
+@item struct timeval ut_tv
+Time the entry was made. For entries of type @code{OLD_TIME} this is
+the time when the system clock changed, and for entries of type
+@code{NEW_TIME} this is the time the system clock was set to.
+
+@item int32_t ut_addr_v6[4]
+The Internet address of a remote host.
+@end table
+@end deftp
+
+The @code{ut_type}, @code{ut_pid}, @code{ut_id}, @code{ut_tv}, and
+@code{ut_host} fields are not available on all systems. Portable
+applications therefore should be prepared for these situations. To help
+doing this the @file{utmp.h} header provides macros
+@code{_HAVE_UT_TYPE}, @code{_HAVE_UT_PID}, @code{_HAVE_UT_ID},
+@code{_HAVE_UT_TV}, and @code{_HAVE_UT_HOST} if the respective field is
+available. The programmer can handle the situations by using
+@code{#ifdef} in the program code.
+
+The following macros are defined for use as values for the
+@code{ut_type} member of the @code{utmp} structure. The values are
+integer constants.
+
+@table @code
+@comment utmp.h
+@comment SVID
+@vindex EMPTY
+@item EMPTY
+This macro is used to indicate that the entry contains no valid user
+accounting information.
+
+@comment utmp.h
+@comment SVID
+@vindex RUN_LVL
+@item RUN_LVL
+This macro is used to identify the systems runlevel.
+
+@comment utmp.h
+@comment SVID
+@vindex BOOT_TIME
+@item BOOT_TIME
+This macro is used to identify the time of system boot.
+
+@comment utmp.h
+@comment SVID
+@vindex OLD_TIME
+@item OLD_TIME
+This macro is used to identify the time when the system clock changed.
+
+@comment utmp.h
+@comment SVID
+@vindex NEW_TIME
+@item NEW_TIME
+This macro is used to identify the time after the system changed.
+
+@comment utmp.h
+@comment SVID
+@vindex INIT_PROCESS
+@item INIT_PROCESS
+This macro is used to identify a process spawned by the init process.
+
+@comment utmp.h
+@comment SVID
+@vindex LOGIN_PROCESS
+@item LOGIN_PROCESS
+This macro is used to identify the session leader of a logged in user.
+
+@comment utmp.h
+@comment SVID
+@vindex USER_PROCESS
+@item USER_PROCESS
+This macro is used to identify a user process.
+
+@comment utmp.h
+@comment SVID
+@vindex DEAD_PROCESS
+@item DEAD_PROCESS
+This macro is used to identify a terminated process.
+
+@comment utmp.h
+@comment SVID
+@vindex ACCOUNTING
+@item ACCOUNTING
+???
+@end table
+
+The size of the @code{ut_line}, @code{ut_id}, @code{ut_user} and
+@code{ut_host} arrays can be found using the @code{sizeof} operator.
+
+Many older systems have, instead of an @code{ut_tv} member, an
+@code{ut_time} member, usually of type @code{time_t}, for representing
+the time associated with the entry. Therefore, for backwards
+compatibility only, @file{utmp.h} defines @code{ut_time} as an alias for
+@code{ut_tv.tv_sec}.
+
+@comment utmp.h
+@comment SVID
+@deftypefun void setutent (void)
+This function opens the user accounting database to begin scanning it.
+You can then call @code{getutent}, @code{getutid} or @code{getutline} to
+read entries and @code{pututline} to write entries.
+
+If the database is already open, it resets the input to the beginning of
+the database.
+@end deftypefun
+
+@comment utmp.h
+@comment SVID
+@deftypefun {struct utmp *} getutent (void)
+The @code{getutent} function reads the next entry from the user
+accounting database. It returns a pointer to the entry, which is
+statically allocated and may be overwritten by subsequent calls to
+@code{getutent}. You must copy the contents of the structure if you
+wish to save the information or you can use the @code{getutent_r}
+function which stores the data in a user-provided buffer.
+
+A null pointer is returned in case no further entry is available.
+@end deftypefun
+
+@comment utmp.h
+@comment SVID
+@deftypefun void endutent (void)
+This function closes the user accounting database.
+@end deftypefun
+
+@comment utmp.h
+@comment SVID
+@deftypefun {struct utmp *} getutid (const struct utmp *@var{id})
+This function searches forward from the current point in the database
+for an entry that matches @var{id}. If the @code{ut_type} member of the
+@var{id} structure is one of @code{RUN_LVL}, @code{BOOT_TIME},
+@code{OLD_TIME} or @code{NEW_TIME} the entries match if the
+@code{ut_type} members are identical. If the @code{ut_type} member of
+the @var{id} structure is @code{INIT_PROCESS}, @code{LOGIN_PROCESS},
+@code{USER_PROCESS} or @code{DEAD_PROCESS}, the entries match if the
+@code{ut_type} member of the entry read from the database is one of
+these four, and the @code{ut_id} members match. However if the
+@code{ut_id} member of either the @var{id} structure or the entry read
+from the database is empty it checks if the @code{ut_line} members match
+instead. If a matching entry is found, @code{getutid} returns a pointer
+to the entry, which is statically allocated, and may be overwritten by a
+subsequent call to @code{getutent}, @code{getutid} or @code{getutline}.
+You must copy the contents of the structure if you wish to save the
+information.
+
+A null pointer is returned in case the end of the database is reached
+without a match.
+
+The @code{getutid} function may cache the last read entry. Therefore,
+if you are using @code{getutid} to search for multiple occurrences, it
+is necessary to zero out the static data after each call. Otherwise
+@code{getutid} could just return a pointer to the same entry over and
+over again.
+@end deftypefun
+
+@comment utmp.h
+@comment SVID
+@deftypefun {struct utmp *} getutline (const struct utmp *@var{line})
+This function searches forward from the current point in the database
+until it finds an entry whose @code{ut_type} value is
+@code{LOGIN_PROCESS} or @code{USER_PROCESS}, and whose @code{ut_line}
+member matches the @code{ut_line} member of the @var{line} structure.
+If it finds such an entry, it returns a pointer to the entry which is
+statically allocated, and may be overwritten by a subsequent call to
+@code{getutent}, @code{getutid} or @code{getutline}. You must copy the
+contents of the structure if you wish to save the information.
+
+A null pointer is returned in case the end of the database is reached
+without a match.
+
+The @code{getutline} function may cache the last read entry. Therefore
+if you are using @code{getutline} to search for multiple occurrences, it
+is necessary to zero out the static data after each call. Otherwise
+@code{getutline} could just return a pointer to the same entry over and
+over again.
+@end deftypefun
+
+@comment utmp.h
+@comment SVID
+@deftypefun {struct utmp *} pututline (const struct utmp *@var{utmp})
+The @code{pututline} function inserts the entry @code{*@var{utmp}} at
+the appropriate place in the user accounting database. If it finds that
+it is not already at the correct place in the database, it uses
+@code{getutid} to search for the position to insert the entry, however
+this will not modify the static structure returned by @code{getutent},
+@code{getutid} and @code{getutline}. If this search fails, the entry
+is appended to the database.
+
+The @code{pututline} function returns a pointer to a copy of the entry
+inserted in the user accounting database, or a null pointer if the entry
+could not be added. The following @code{errno} error conditions are
+defined for this function:
+
+@table @code
+@item EPERM
+The process does not have the appropriate privileges; you cannot modify
+the user accounting database.
+@end table
+@end deftypefun
+
+All the @code{get*} functions mentioned before store the information
+they return in a static buffer. This can be a problem in multi-threaded
+programs since the data returned for the request is overwritten by the
+return value data in another thread. Therefore @theglibc{}
+provides as extensions three more functions which return the data in a
+user-provided buffer.
+
+@comment utmp.h
+@comment GNU
+@deftypefun int getutent_r (struct utmp *@var{buffer}, struct utmp **@var{result})
+The @code{getutent_r} is equivalent to the @code{getutent} function. It
+returns the next entry from the database. But instead of storing the
+information in a static buffer it stores it in the buffer pointed to by
+the parameter @var{buffer}.
+
+If the call was successful, the function returns @code{0} and the
+pointer variable pointed to by the parameter @var{result} contains a
+pointer to the buffer which contains the result (this is most probably
+the same value as @var{buffer}). If something went wrong during the
+execution of @code{getutent_r} the function returns @code{-1}.
+
+This function is a GNU extension.
+@end deftypefun
+
+@comment utmp.h
+@comment GNU
+@deftypefun int getutid_r (const struct utmp *@var{id}, struct utmp *@var{buffer}, struct utmp **@var{result})
+This function retrieves just like @code{getutid} the next entry matching
+the information stored in @var{id}. But the result is stored in the
+buffer pointed to by the parameter @var{buffer}.
+
+If successful the function returns @code{0} and the pointer variable
+pointed to by the parameter @var{result} contains a pointer to the
+buffer with the result (probably the same as @var{result}. If not
+successful the function return @code{-1}.
+
+This function is a GNU extension.
+@end deftypefun
+
+@comment utmp.h
+@comment GNU
+@deftypefun int getutline_r (const struct utmp *@var{line}, struct utmp *@var{buffer}, struct utmp **@var{result})
+This function retrieves just like @code{getutline} the next entry
+matching the information stored in @var{line}. But the result is stored
+in the buffer pointed to by the parameter @var{buffer}.
+
+If successful the function returns @code{0} and the pointer variable
+pointed to by the parameter @var{result} contains a pointer to the
+buffer with the result (probably the same as @var{result}. If not
+successful the function return @code{-1}.
+
+This function is a GNU extension.
+@end deftypefun
+
+
+In addition to the user accounting database, most systems keep a number
+of similar databases. For example most systems keep a log file with all
+previous logins (usually in @file{/etc/wtmp} or @file{/var/log/wtmp}).
+
+For specifying which database to examine, the following function should
+be used.
+
+@comment utmp.h
+@comment SVID
+@deftypefun int utmpname (const char *@var{file})
+The @code{utmpname} function changes the name of the database to be
+examined to @var{file}, and closes any previously opened database. By
+default @code{getutent}, @code{getutid}, @code{getutline} and
+@code{pututline} read from and write to the user accounting database.
+
+The following macros are defined for use as the @var{file} argument:
+
+@deftypevr Macro {char *} _PATH_UTMP
+This macro is used to specify the user accounting database.
+@end deftypevr
+
+@deftypevr Macro {char *} _PATH_WTMP
+This macro is used to specify the user accounting log file.
+@end deftypevr
+
+The @code{utmpname} function returns a value of @code{0} if the new name
+was successfully stored, and a value of @code{-1} to indicate an error.
+Note that @code{utmpname} does not try to open the database, and that
+therefore the return value does not say anything about whether the
+database can be successfully opened.
+@end deftypefun
+
+Specially for maintaining log-like databases @theglibc{} provides
+the following function:
+
+@comment utmp.h
+@comment SVID
+@deftypefun void updwtmp (const char *@var{wtmp_file}, const struct utmp *@var{utmp})
+The @code{updwtmp} function appends the entry *@var{utmp} to the
+database specified by @var{wtmp_file}. For possible values for the
+@var{wtmp_file} argument see the @code{utmpname} function.
+@end deftypefun
+
+@strong{Portability Note:} Although many operating systems provide a
+subset of these functions, they are not standardized. There are often
+subtle differences in the return types, and there are considerable
+differences between the various definitions of @code{struct utmp}. When
+programming for @theglibc{}, it is probably best to stick
+with the functions described in this section. If however, you want your
+program to be portable, consider using the XPG functions described in
+@ref{XPG Functions}, or take a look at the BSD compatible functions in
+@ref{Logging In and Out}.
+
+
+@node XPG Functions
+@subsection XPG User Accounting Database Functions
+
+These functions, described in the X/Open Portability Guide, are declared
+in the header file @file{utmpx.h}.
+@pindex utmpx.h
+
+@deftp {Data Type} {struct utmpx}
+The @code{utmpx} data structure contains at least the following members:
+
+@table @code
+@item short int ut_type
+Specifies the type of login; one of @code{EMPTY}, @code{RUN_LVL},
+@code{BOOT_TIME}, @code{OLD_TIME}, @code{NEW_TIME}, @code{INIT_PROCESS},
+@code{LOGIN_PROCESS}, @code{USER_PROCESS} or @code{DEAD_PROCESS}.
+
+@item pid_t ut_pid
+The process ID number of the login process.
+
+@item char ut_line[]
+The device name of the tty (without @file{/dev/}).
+
+@item char ut_id[]
+The inittab ID of the process.
+
+@item char ut_user[]
+The user's login name.
+
+@item struct timeval ut_tv
+Time the entry was made. For entries of type @code{OLD_TIME} this is
+the time when the system clock changed, and for entries of type
+@code{NEW_TIME} this is the time the system clock was set to.
+@end table
+In @theglibc{}, @code{struct utmpx} is identical to @code{struct
+utmp} except for the fact that including @file{utmpx.h} does not make
+visible the declaration of @code{struct exit_status}.
+@end deftp
+
+The following macros are defined for use as values for the
+@code{ut_type} member of the @code{utmpx} structure. The values are
+integer constants and are, in @theglibc{}, identical to the
+definitions in @file{utmp.h}.
+
+@table @code
+@comment utmpx.h
+@comment XPG4.2
+@vindex EMPTY
+@item EMPTY
+This macro is used to indicate that the entry contains no valid user
+accounting information.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex RUN_LVL
+@item RUN_LVL
+This macro is used to identify the systems runlevel.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex BOOT_TIME
+@item BOOT_TIME
+This macro is used to identify the time of system boot.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex OLD_TIME
+@item OLD_TIME
+This macro is used to identify the time when the system clock changed.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex NEW_TIME
+@item NEW_TIME
+This macro is used to identify the time after the system changed.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex INIT_PROCESS
+@item INIT_PROCESS
+This macro is used to identify a process spawned by the init process.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex LOGIN_PROCESS
+@item LOGIN_PROCESS
+This macro is used to identify the session leader of a logged in user.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex USER_PROCESS
+@item USER_PROCESS
+This macro is used to identify a user process.
+
+@comment utmpx.h
+@comment XPG4.2
+@vindex DEAD_PROCESS
+@item DEAD_PROCESS
+This macro is used to identify a terminated process.
+@end table
+
+The size of the @code{ut_line}, @code{ut_id} and @code{ut_user} arrays
+can be found using the @code{sizeof} operator.
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun void setutxent (void)
+This function is similar to @code{setutent}. In @theglibc{} it is
+simply an alias for @code{setutent}.
+@end deftypefun
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun {struct utmpx *} getutxent (void)
+The @code{getutxent} function is similar to @code{getutent}, but returns
+a pointer to a @code{struct utmpx} instead of @code{struct utmp}. In
+@theglibc{} it simply is an alias for @code{getutent}.
+@end deftypefun
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun void endutxent (void)
+This function is similar to @code{endutent}. In @theglibc{} it is
+simply an alias for @code{endutent}.
+@end deftypefun
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun {struct utmpx *} getutxid (const struct utmpx *@var{id})
+This function is similar to @code{getutid}, but uses @code{struct utmpx}
+instead of @code{struct utmp}. In @theglibc{} it is simply an alias
+for @code{getutid}.
+@end deftypefun
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun {struct utmpx *} getutxline (const struct utmpx *@var{line})
+This function is similar to @code{getutid}, but uses @code{struct utmpx}
+instead of @code{struct utmp}. In @theglibc{} it is simply an alias
+for @code{getutline}.
+@end deftypefun
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun {struct utmpx *} pututxline (const struct utmpx *@var{utmp})
+The @code{pututxline} function is functionally identical to
+@code{pututline}, but uses @code{struct utmpx} instead of @code{struct
+utmp}. In @theglibc{}, @code{pututxline} is simply an alias for
+@code{pututline}.
+@end deftypefun
+
+@comment utmpx.h
+@comment XPG4.2
+@deftypefun int utmpxname (const char *@var{file})
+The @code{utmpxname} function is functionally identical to
+@code{utmpname}. In @theglibc{}, @code{utmpxname} is simply an
+alias for @code{utmpname}.
+@end deftypefun
+
+You can translate between a traditional @code{struct utmp} and an XPG
+@code{struct utmpx} with the following functions. In @theglibc{},
+these functions are merely copies, since the two structures are
+identical.
+
+@comment utmpx.h
+@comment utmp.h
+@comment GNU
+@deftypefun int getutmp (const struct utmpx *@var{utmpx}, struct utmp *@var{utmp})
+@code{getutmp} copies the information, insofar as the structures are
+compatible, from @var{utmpx} to @var{utmp}.
+@end deftypefun
+
+@comment utmpx.h
+@comment utmp.h
+@comment GNU
+@deftypefun int getutmpx (const struct utmp *@var{utmp}, struct utmpx *@var{utmpx})
+@code{getutmpx} copies the information, insofar as the structures are
+compatible, from @var{utmp} to @var{utmpx}.
+@end deftypefun
+
+
+@node Logging In and Out
+@subsection Logging In and Out
+
+These functions, derived from BSD, are available in the separate
+@file{libutil} library, and declared in @file{utmp.h}.
+@pindex utmp.h
+
+Note that the @code{ut_user} member of @code{struct utmp} is called
+@code{ut_name} in BSD. Therefore, @code{ut_name} is defined as an alias
+for @code{ut_user} in @file{utmp.h}.
+
+@comment utmp.h
+@comment BSD
+@deftypefun int login_tty (int @var{filedes})
+This function makes @var{filedes} the controlling terminal of the
+current process, redirects standard input, standard output and
+standard error output to this terminal, and closes @var{filedes}.
+
+This function returns @code{0} on successful completion, and @code{-1}
+on error.
+@end deftypefun
+
+@comment utmp.h
+@comment BSD
+@deftypefun void login (const struct utmp *@var{entry})
+The @code{login} functions inserts an entry into the user accounting
+database. The @code{ut_line} member is set to the name of the terminal
+on standard input. If standard input is not a terminal @code{login}
+uses standard output or standard error output to determine the name of
+the terminal. If @code{struct utmp} has a @code{ut_type} member,
+@code{login} sets it to @code{USER_PROCESS}, and if there is an
+@code{ut_pid} member, it will be set to the process ID of the current
+process. The remaining entries are copied from @var{entry}.
+
+A copy of the entry is written to the user accounting log file.
+@end deftypefun
+
+@comment utmp.h
+@comment BSD
+@deftypefun int logout (const char *@var{ut_line})
+This function modifies the user accounting database to indicate that the
+user on @var{ut_line} has logged out.
+
+The @code{logout} function returns @code{1} if the entry was successfully
+written to the database, or @code{0} on error.
+@end deftypefun
+
+@comment utmp.h
+@comment BSD
+@deftypefun void logwtmp (const char *@var{ut_line}, const char *@var{ut_name}, const char *@var{ut_host})
+The @code{logwtmp} function appends an entry to the user accounting log
+file, for the current time and the information provided in the
+@var{ut_line}, @var{ut_name} and @var{ut_host} arguments.
+@end deftypefun
+
+@strong{Portability Note:} The BSD @code{struct utmp} only has the
+@code{ut_line}, @code{ut_name}, @code{ut_host} and @code{ut_time}
+members. Older systems do not even have the @code{ut_host} member.
+
+
+@node User Database
@section User Database
@cindex user database
@cindex password database
@pindex /etc/passwd
-This section describes all about how to search and scan the database of
-registered users. The database itself is kept in the file
-@file{/etc/passwd} on most systems, but on some systems a special
-network server gives access to it.
+This section describes how to search and scan the database of registered
+users. The database itself is kept in the file @file{/etc/passwd} on
+most systems, but on some systems a special network server gives access
+to it.
@menu
* User Data Structure:: What each user record contains.
* Writing a User Entry:: How a program can rewrite a user's record.
@end menu
-@node User Data Structure, Lookup User, User Database, User Database
+@node User Data Structure
@subsection The Data Structure that Describes a User
The functions and data structures for accessing the system user database
@end table
@end deftp
-@node Lookup User, Scanning All Users, User Data Structure, User Database
+@node Lookup User
@subsection Looking Up One User
@cindex converting user ID to user name
@cindex converting user name to user ID
@comment pwd.h
@comment POSIX.1c
@deftypefun int getpwuid_r (uid_t @var{uid}, struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
-This function is similar to @code{getpwuid} in that is returns
-information about the user whose user ID is @var{uid}. But the result
-is not placed in a static buffer. Instead the user supplied structure
-pointed to by @var{result_buf} is filled with the information. The
-first @var{buflen} bytes of the additional buffer pointed to by
-@var{buffer} are used to contain additional information, normally
-strings which are pointed to by the elements of the result structure.
-
-If the return value is @code{0} the pointer returned in @var{result}
-points to the record which contains the wanted data (i.e., @var{result}
-contains the value @var{result_buf}). In case the return value is non
-null there is no user in the data base with user ID @var{uid} or the
-buffer @var{buffer} is too small to contain all the needed information.
-In the later case the global @var{errno} variable is set to
+This function is similar to @code{getpwuid} in that it returns
+information about the user whose user ID is @var{uid}. However, it
+fills the user supplied structure pointed to by @var{result_buf} with
+the information instead of using a static buffer. The first
+@var{buflen} bytes of the additional buffer pointed to by @var{buffer}
+are used to contain additional information, normally strings which are
+pointed to by the elements of the result structure.
+
+If a user with ID @var{uid} is found, the pointer returned in
+@var{result} points to the record which contains the wanted data (i.e.,
+@var{result} contains the value @var{result_buf}). If no user is found
+or if an error occurred, the pointer returned in @var{result} is a null
+pointer. The function returns zero or an error code. If the buffer
+@var{buffer} is too small to contain all the needed information, the
+error code @code{ERANGE} is returned and @var{errno} is set to
@code{ERANGE}.
@end deftypefun
This structure may be overwritten on subsequent calls to
@code{getpwnam}.
-A null pointer value indicates there is no user named @var{name}.
+A null pointer return indicates there is no user named @var{name}.
@end deftypefun
@comment pwd.h
@comment POSIX.1c
@deftypefun int getpwnam_r (const char *@var{name}, struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
This function is similar to @code{getpwnam} in that is returns
-information about the user whose user name is @var{name}. But the result
-is not placed in a static buffer. Instead the user supplied structure
-pointed to by @var{result_buf} is filled with the information. The
-first @var{buflen} bytes of the additional buffer pointed to by
-@var{buffer} are used to contain additional information, normally
-strings which are pointed to by the elements of the result structure.
+information about the user whose user name is @var{name}. However, like
+@code{getpwuid_r}, it fills the user supplied buffers in
+@var{result_buf} and @var{buffer} with the information instead of using
+a static buffer.
-If the return value is @code{0} the pointer returned in @var{result}
-points to the record which contains the wanted data (i.e., @var{result}
-contains the value @var{result_buf}). In case the return value is non
-null there is no user in the data base with user name @var{name} or the
-buffer @var{buffer} is too small to contain all the needed information.
-In the later case the global @var{errno} variable is set to
-@code{ERANGE}.
+The return values are the same as for @code{getpwuid_r}.
@end deftypefun
-@node Scanning All Users, Writing a User Entry, Lookup User, User Database
+@node Scanning All Users
@subsection Scanning the List of All Users
@cindex scanning the user list
rewritten on subsequent calls to @code{fgetpwent}. You must copy the
contents of the structure if you wish to save the information.
-This stream must correspond to a file in the same format as the standard
-password database file. This function comes from System V.
+The stream must correspond to a file in the same format as the standard
+password database file.
@end deftypefun
@comment pwd.h
@var{buffer} are used to contain additional information, normally
strings which are pointed to by the elements of the result structure.
-This stream must correspond to a file in the same format as the standard
+The stream must correspond to a file in the same format as the standard
password database file.
-If the function returns null @var{result} points to the structure with
+If the function returns zero @var{result} points to the structure with
the wanted data (normally this is in @var{result_buf}). If errors
-occured the return value is non-null and @var{result} contains a null
+occurred the return value is nonzero and @var{result} contains a null
pointer.
@end deftypefun
to @code{getpwent}. You must copy the contents of the structure if you
wish to save the information.
-A null pointer is returned in case no further entry is available.
+A null pointer is returned when no more entries are available.
@end deftypefun
@comment pwd.h
@comment GNU
-@deftypefun int getpwent_r (struct passwd *@var{result_buf}, char *@var{buffer}, int @var{buflen}, struct passwd **@var{result})
+@deftypefun int getpwent_r (struct passwd *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct passwd **@var{result})
This function is similar to @code{getpwent} in that it returns the next
-entry from the stream initialized by @code{setpwent}. But in contrast
-to the @code{getpwent} function this function is reentrant since the
-result is placed in the user supplied structure pointed to by
-@var{result_buf}. Additional data, normally the strings pointed to by
-the elements of the result structure, are placed in the additional
-buffer or length @var{buflen} starting at @var{buffer}.
+entry from the stream initialized by @code{setpwent}. Like
+@code{fgetpwent_r}, it uses the user-supplied buffers in
+@var{result_buf} and @var{buffer} to return the information requested.
+
+The return values are the same as for @code{fgetpwent_r}.
-If the function returns zero @var{result} points to the structure with
-the wanted data (normally this is in @var{result_buf}). If errors
-occured the return value is non-zero and @var{result} contains a null
-pointer.
@end deftypefun
@comment pwd.h
@code{getpwent_r}.
@end deftypefun
-@node Writing a User Entry, , Scanning All Users, User Database
+@node Writing a User Entry
@subsection Writing a User Entry
@comment pwd.h
on a system which merges the traditional Unix data base with other
extended information about users, adding an entry using this function
would inevitably leave out much of the important information.
+@c Then how are programmers to modify the password file? -zw
+
+The group and user ID fields are left empty if the group or user name
+starts with a - or +.
The function @code{putpwent} is declared in @file{pwd.h}.
@end deftypefun
-@node Group Database, Netgroup Database, User Database, Users and Groups
+@node Group Database
@section Group Database
@cindex group database
@pindex /etc/group
-This section describes all about how to search and scan the database of
+This section describes how to search and scan the database of
registered groups. The database itself is kept in the file
@file{/etc/group} on most systems, but on some systems a special network
service provides access to it.
* Scanning All Groups:: Scanning the list of all groups.
@end menu
-@node Group Data Structure, Lookup Group, Group Database, Group Database
+@node Group Data Structure
@subsection The Data Structure for a Group
The functions and data structures for accessing the system group
@end table
@end deftp
-@node Lookup Group, Scanning All Groups, Group Data Structure, Group Database
+@node Lookup Group
@subsection Looking Up One Group
@cindex converting group name to group ID
@cindex converting group ID to group name
@comment grp.h
@comment POSIX.1c
@deftypefun int getgrgid_r (gid_t @var{gid}, struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
-This function is similar to @code{getgrgid} in that is returns
-information about the group whose group ID is @var{gid}. But the result
-is not placed in a static buffer. Instead the user supplied structure
-pointed to by @var{result_buf} is filled with the information. The
-first @var{buflen} bytes of the additional buffer pointed to by
-@var{buffer} are used to contain additional information, normally
-strings which are pointed to by the elements of the result structure.
-
-If the return value is @code{0} the pointer returned in @var{result}
-points to the record which contains the wanted data (i.e., @var{result}
-contains the value @var{result_buf}). If the return value is non-zero
-there is no group in the data base with group ID @var{gid} or the
-buffer @var{buffer} is too small to contain all the needed information.
-In the later case the global @var{errno} variable is set to
+This function is similar to @code{getgrgid} in that it returns
+information about the group whose group ID is @var{gid}. However, it
+fills the user supplied structure pointed to by @var{result_buf} with
+the information instead of using a static buffer. The first
+@var{buflen} bytes of the additional buffer pointed to by @var{buffer}
+are used to contain additional information, normally strings which are
+pointed to by the elements of the result structure.
+
+If a group with ID @var{gid} is found, the pointer returned in
+@var{result} points to the record which contains the wanted data (i.e.,
+@var{result} contains the value @var{result_buf}). If no group is found
+or if an error occurred, the pointer returned in @var{result} is a null
+pointer. The function returns zero or an error code. If the buffer
+@var{buffer} is too small to contain all the needed information, the
+error code @code{ERANGE} is returned and @var{errno} is set to
@code{ERANGE}.
@end deftypefun
@comment POSIX.1c
@deftypefun int getgrnam_r (const char *@var{name}, struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
This function is similar to @code{getgrnam} in that is returns
-information about the group whose group name is @var{name}. But the result
-is not placed in a static buffer. Instead the user supplied structure
-pointed to by @var{result_buf} is filled with the information. The
-first @var{buflen} bytes of the additional buffer pointed to by
-@var{buffer} are used to contain additional information, normally
-strings which are pointed to by the elements of the result structure.
+information about the group whose group name is @var{name}. Like
+@code{getgrgid_r}, it uses the user supplied buffers in
+@var{result_buf} and @var{buffer}, not a static buffer.
-If the return value is @code{0} the pointer returned in @var{result}
-points to the record which contains the wanted data (i.e., @var{result}
-contains the value @var{result_buf}). If the return value is non-zero
-there is no group in the data base with group name @var{name} or the
-buffer @var{buffer} is too small to contain all the needed information.
-In the later case the global @var{errno} variable is set to
+The return values are the same as for @code{getgrgid_r}
@code{ERANGE}.
@end deftypefun
-@node Scanning All Groups, , Lookup Group, Group Database
+@node Scanning All Groups
@subsection Scanning the List of All Groups
@cindex scanning the group list
@deftypefun {struct group *} fgetgrent (FILE *@var{stream})
The @code{fgetgrent} function reads the next entry from @var{stream}.
It returns a pointer to the entry. The structure is statically
-allocated and is rewritten on subsequent calls to @code{fgetgrent}. You
+allocated and is overwritten on subsequent calls to @code{fgetgrent}. You
must copy the contents of the structure if you wish to save the
information.
@deftypefun int fgetgrent_r (FILE *@var{stream}, struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
This function is similar to @code{fgetgrent} in that it reads the next
user entry from @var{stream}. But the result is returned in the
-structure pointed to by @var{result_buf}. The
-first @var{buflen} bytes of the additional buffer pointed to by
-@var{buffer} are used to contain additional information, normally
-strings which are pointed to by the elements of the result structure.
+structure pointed to by @var{result_buf}. The first @var{buflen} bytes
+of the additional buffer pointed to by @var{buffer} are used to contain
+additional information, normally strings which are pointed to by the
+elements of the result structure.
This stream must correspond to a file in the same format as the standard
group database file.
If the function returns zero @var{result} points to the structure with
the wanted data (normally this is in @var{result_buf}). If errors
-occured the return value is non-zero and @var{result} contains a null
+occurred the return value is non-zero and @var{result} contains a null
pointer.
@end deftypefun
@deftypefun {struct group *} getgrent (void)
The @code{getgrent} function reads the next entry from the stream
initialized by @code{setgrent}. It returns a pointer to the entry. The
-structure is statically allocated and is rewritten on subsequent calls
+structure is statically allocated and is overwritten on subsequent calls
to @code{getgrent}. You must copy the contents of the structure if you
wish to save the information.
@end deftypefun
@comment GNU
@deftypefun int getgrent_r (struct group *@var{result_buf}, char *@var{buffer}, size_t @var{buflen}, struct group **@var{result})
This function is similar to @code{getgrent} in that it returns the next
-entry from the stream initialized by @code{setgrent}. But in contrast
-to the @code{getgrent} function this function is reentrant since the
-result is placed in the user supplied structure pointed to by
-@var{result_buf}. Additional data, normally the strings pointed to by
-the elements of the result structure, are placed in the additional
-buffer or length @var{buflen} starting at @var{buffer}.
+entry from the stream initialized by @code{setgrent}. Like
+@code{fgetgrent_r}, it places the result in user-supplied buffers
+pointed to @var{result_buf} and @var{buffer}.
-If the function returns zero @var{result} points to the structure with
-the wanted data (normally this is in @var{result_buf}). If errors
-occured the return value is non-zero and @var{result} contains a null
-pointer.
+If the function returns zero @var{result} contains a pointer to the data
+(normally equal to @var{result_buf}). If errors occurred the return
+value is non-zero and @var{result} contains a null pointer.
@end deftypefun
@comment grp.h
@code{getgrent_r}.
@end deftypefun
-@node Netgroup Database, Database Example, Group Database, Users and Groups
+@node Database Example
+@section User and Group Database Example
+
+Here is an example program showing the use of the system database inquiry
+functions. The program prints some information about the user running
+the program.
+
+@smallexample
+@include db.c.texi
+@end smallexample
+
+Here is some output from this program:
+
+@smallexample
+I am Throckmorton Snurd.
+My login name is snurd.
+My uid is 31093.
+My home directory is /home/fsg/snurd.
+My default shell is /bin/sh.
+My default group is guest (12).
+The members of this group are:
+ friedman
+ tami
+@end smallexample
+
+@node Netgroup Database
@section Netgroup Database
@menu
* Netgroup Membership:: How to test for netgroup membership.
@end menu
-@node Netgroup Data, Lookup Netgroup, Netgroup Database, Netgroup Database
+@node Netgroup Data
@subsection Netgroup Data
@cindex Netgroup
-Sometimes it is useful group users according to other criterias like the
-ones used in the @xref{Group Database}. E.g., it is useful to associate
-a certain group of users with a certain machine. On the other hand
-grouping of host names is not supported so far.
+Sometimes it is useful to group users according to other criteria
+(@pxref{Group Database}). E.g., it is useful to associate a certain
+group of users with a certain machine. On the other hand grouping of
+host names is not supported so far.
In Sun Microsystems SunOS appeared a new kind of database, the netgroup
-database. It allows to group hosts, users, and domain freely, giving
-them individual names. More concrete: a netgroup is a list of triples
-consisting of a host name, a user name, and a domain name, where any of
-the entries can be a wildcard entry, matching all inputs. A last
+database. It allows grouping hosts, users, and domains freely, giving
+them individual names. To be more concrete, a netgroup is a list of triples
+consisting of a host name, a user name, and a domain name where any of
+the entries can be a wildcard entry matching all inputs. A last
possibility is that names of other netgroups can also be given in the
-list specifying a netgroup. So one can construct arbitrary hierachies
+list specifying a netgroup. So one can construct arbitrary hierarchies
without loops.
Sun's implementation allows netgroups only for the @code{nis} or
-@code{nisplus} service @pxref{Services in the NSS configuration}. The
-implementation in the GNU C library has no such restriction. An entry
+@code{nisplus} service, @pxref{Services in the NSS configuration}. The
+implementation in @theglibc{} has no such restriction. An entry
in either of the input services must have the following form:
@smallexample
Any of the fields in the triple can be empty which means anything
matches. While describing the functions we will see that the opposite
case is useful as well. I.e., there may be entries which will not
-match any input. For entries like a name consisting of the single
+match any input. For entries like this, a name consisting of the single
character @code{-} shall be used.
-@node Lookup Netgroup, Netgroup Membership, Netgroup Data, Netgroup Database
+@node Lookup Netgroup
@subsection Looking up one Netgroup
The lookup functions for netgroups are a bit different to all other
These functions are declared in @file{netdb.h}.
@comment netdb.h
+@comment BSD
@deftypefun int setnetgrent (const char *@var{netgroup})
A call to this function initializes the internal state of the library to
-allow following calls of the @code{getnetgrent} iterate over all entries
+allow following calls of the @code{getnetgrent} to iterate over all entries
in the netgroup with name @var{netgroup}.
-When the call is successful (i.e., when a netgroup with this name exist)
+When the call is successful (i.e., when a netgroup with this name exists)
the return value is @code{1}. When the return value is @code{0} no
-netgroup of this name is known or some other error occured.
+netgroup of this name is known or some other error occurred.
@end deftypefun
It is important to remember that there is only one single state for
@code{compat} service part of the NSS implementation.
@comment netdb.h
+@comment BSD
@deftypefun int getnetgrent (char **@var{hostp}, char **@var{userp}, char **@var{domainp})
This function returns the next unprocessed entry of the currently
-selected netgroup. The string pointers, which addresses are passed in
+selected netgroup. The string pointers, in which addresses are passed in
the arguments @var{hostp}, @var{userp}, and @var{domainp}, will contain
after a successful call pointers to appropriate strings. If the string
in the next entry is empty the pointer has the value @code{NULL}.
-The returned string pointers are only valid unless no of the netgroup
+The returned string pointers are only valid if none of the netgroup
related functions are called.
The return value is @code{1} if the next entry was successfully read. A
-value of @code{0} means no further entry exist or internal errors occured.
+value of @code{0} means no further entries exist or internal errors occurred.
@end deftypefun
@comment netdb.h
-@deftypefun int getnetgrent_r (char **@var{hostp}, char **@var{userp}, char **@var{domainp}, char *@var{buffer}, int @var{buflen})
+@comment GNU
+@deftypefun int getnetgrent_r (char **@var{hostp}, char **@var{userp}, char **@var{domainp}, char *@var{buffer}, size_t @var{buflen})
This function is similar to @code{getnetgrent} with only one exception:
the strings the three string pointers @var{hostp}, @var{userp}, and
@var{domainp} point to, are placed in the buffer of @var{buflen} bytes
The return value is @code{1} if the next entry was successfully read and
the buffer contains enough room to place the strings in it. @code{0} is
returned in case no more entries are found, the buffer is too small, or
-internal errors occured.
+internal errors occurred.
This function is a GNU extension. The original implementation in the
SunOS libc does not provide this function.
@end deftypefun
@comment netdb.h
+@comment BSD
@deftypefun void endnetgrent (void)
-This function free all buffers which were allocated to process the last
+This function frees all buffers which were allocated to process the last
selected netgroup. As a result all string pointers returned by calls
to @code{getnetgrent} are invalid afterwards.
@end deftypefun
-@node Netgroup Membership, , Lookup Netgroup, Netgroup Database
+@node Netgroup Membership
@subsection Testing for Netgroup Membership
It is often not necessary to scan the whole netgroup since often the
selected netgroup.
@comment netdb.h
+@comment BSD
@deftypefun int innetgr (const char *@var{netgroup}, const char *@var{host}, const char *@var{user}, const char *@var{domain})
This function tests whether the triple specified by the parameters
@var{hostp}, @var{userp}, and @var{domainp} is part of the netgroup
@end enumerate
Any of the pointers @var{hostp}, @var{userp}, and @var{domainp} can be
-@code{NULL} which means any value is excepted in this position. This is
+@code{NULL} which means any value is accepted in this position. This is
also true for the name @code{-} which should not match any other string
otherwise.
The return value is @code{1} if an entry matching the given triple is
found in the netgroup. The return value is @code{0} if the netgroup
itself is not found, the netgroup does not contain the triple or
-internal errors occured.
+internal errors occurred.
@end deftypefun
-
-@node Database Example, , Netgroup Database, Users and Groups
-@section User and Group Database Example
-
-Here is an example program showing the use of the system database inquiry
-functions. The program prints some information about the user running
-the program.
-
-@smallexample
-@include db.c.texi
-@end smallexample
-
-Here is some output from this program:
-
-@smallexample
-I am Throckmorton Snurd.
-My login name is snurd.
-My uid is 31093.
-My home directory is /home/fsg/snurd.
-My default shell is /bin/sh.
-My default group is guest (12).
-The members of this group are:
- friedman
- tami
-@end smallexample
git://sourceware.org / glibc.git / blobdiff