gdbserver is a control program for Unix-like systems, which
allows you to connect your program with a remote gdb via
target remote or
target extended-remote—but without
linking in the usual debugging stub.
gdbserver is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that gdb itself does. In fact, a system that can run
gdbserver to connect to a remote gdb could also run
gdbserver is sometimes useful nevertheless,
because it is a much smaller program than gdb itself. It is
also easier to port than all of gdb, so you may be able to get
started more quickly on a new system by using
Finally, if you develop code for real-time systems, you may find that
the tradeoffs involved in real-time operation make it more convenient to
do as much development work as possible on another system, for example
by cross-compiling. You can use
gdbserver to make a similar
choice for debugging.
gdbserver communicate via either a serial line
or a TCP connection, using the standard gdb remote serial
gdbserverdoes not have any built-in security. Do not run
gdbserverconnected to any public network; a gdb connection to
gdbserverprovides access to the target system with the same privileges as the user running
gdbserver on the target system. You need a copy of the
program you want to debug, including any libraries it requires.
gdbserver does not need your program's symbol table, so you can
strip the program if necessary to save space. gdb on the host
system does all the symbol handling.
To use the server, you must tell it how to communicate with gdb; the name of your program; and the arguments for your program. The usual syntax is:
target> gdbserver comm program [ args ... ]
comm is either a device name (to use a serial line), or a TCP
hostname and portnumber, or
stdio to use
For example, to debug Emacs with the argument
‘foo.txt’ and communicate with gdb over the serial port
target> gdbserver /dev/com1 emacs foo.txt
gdbserver waits passively for the host gdb to communicate
To use a TCP connection instead of a serial line:
target> gdbserver host:2345 emacs foo.txt
The only difference from the previous example is the first argument,
specifying that you are communicating with the host gdb via
TCP. The ‘host:2345’ argument means that
gdbserver is to
expect a TCP connection from machine ‘host’ to local TCP port 2345.
(Currently, the ‘host’ part is ignored.) You can choose any number
you want for the port number as long as it does not conflict with any
TCP ports already in use on the target system (for example,
telnet).1 You must use the same port number with the host gdb
target remote command.
stdio connection is useful when starting
(gdb) target remote | ssh -T hostname gdbserver - hello
The ‘-T’ option to ssh is provided because we don't need a remote pty, and we don't want escape-character handling. Ssh does this by default when a command is provided, the flag is provided to make it explicit. You could elide it if you want to.
Programs started with stdio-connected gdbserver have /dev/null for
stderr are sent back to gdb for
display through a pipe connected to gdbserver.
stderr use the same pipe.
On some targets,
gdbserver can also attach to running programs.
This is accomplished via the
--attach argument. The syntax is:
target> gdbserver --attach comm pid
pid is the process ID of a currently running process. It isn't
necessary to point
gdbserver at a binary for the running process.
target extended-remote mode, you can also attach using the
gdb attach command
(see Attaching in Types of Remote Connections).
You can debug processes by name instead of process ID if your target has the
target> gdbserver --attach comm `pidof program`
In case more than one copy of program is running, or program
has multiple threads, most versions of
pidof support the
-s option to only return the first process ID.
This section applies only when
gdbserver is run to listen on a TCP
gdbserver normally terminates after all of its debugged processes have
terminated in target remote mode. On the other hand, for target
gdbserver stays running even with no processes left.
gdb normally terminates the spawned debugged process on its exit,
which normally also terminates
gdbserver in the target remote
mode. Therefore, when the connection drops unexpectedly, and gdb
gdbserver to kill its debugged processes,
stays running even in the target remote mode.
gdbserver stays running, gdb can connect to it again later.
Such reconnecting is useful for features like disconnected tracing. For
completeness, at most one gdb can be connected at a time.
gdbserver keeps the listening TCP port open, so that
subsequent connections are possible. However, if you start
with the --once option, it will stop listening for any further
connection attempts after connecting to the first gdb session. This
means no further connections to
gdbserver will be possible after the
first one. It also means
gdbserver will terminate after the first
connection with remote gdb has closed, even for unexpectedly closed
connections and even in the target extended-remote mode. The
--once option allows reusing the same port number for connecting to
multiple instances of
gdbserver running on the same host, since each
instance closes its port after the first connection.
You can use the --multi option to start
specifying a program to debug or a process to attach to. Then you can
target extended-remote mode and run or attach to a
program. For more information,
see –multi Option in Types of Remote Connnections.
The --debug option tells
gdbserver to display extra
status information about the debugging process.
The --remote-debug option tells
gdbserver to display
remote protocol debug output. These options are intended for
gdbserver development and for bug reports to the developers.
The --debug-format=option1[,option2,...] option tells
gdbserver to include additional information in each output.
Possible options are:
Options are processed in order. Thus, for example, if none appears last then no additional information is added to debugging output.
The --wrapper option specifies a wrapper to launch programs for debugging. The option should be followed by the name of the wrapper, then any command-line arguments to pass to the wrapper, then -- indicating the end of the wrapper arguments.
gdbserver runs the specified wrapper program with a combined
command line including the wrapper arguments, then the name of the
program to debug, then any arguments to the program. The wrapper
runs until it executes your program, and then gdb gains control.
You can use any program that eventually calls
its arguments as a wrapper. Several standard Unix utilities do
nohup. Any Unix shell script ending
exec "$@" will also work.
For example, you can use
env to pass an environment variable to
the debugged program, without setting the variable in
$ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
The basic procedure for connecting to the remote target is:
filecommand before you connect. Use
set sysrootto locate target libraries (unless your gdb was compiled with the correct sysroot using
gdbserverprior to using the
targetcommand. Otherwise you may get an error whose text depends on the host system, but which usually looks something like ‘Connection refused’. Don't use the
loadcommand in gdb when using
target remotemode, since the program is already on the target.
During a gdb session using
gdbserver, you can use the
monitor command to send special requests to
Here are the available commands.
monitor set debug 0
monitor set debug 1
monitor set remote-debug 0
monitor set remote-debug 1
monitor set debug-format option1[
Options are processed in order. Thus, for example, if none
appears last then no additional information is added to debugging output.
monitor set libthread-db-search-path [PATH]
libthread_db(see set libthread-db-search-path). If you omit path, ‘libthread-db-search-path’ will be reset to its default value.
The special entry ‘$pdir’ for ‘libthread-db-search-path’ is
not supported in
disconnectto close the debugging session.
gdbserverwill detach from any attached processes and kill any processes it created. Use
monitor exitto terminate
gdbserverat the end of a multi-process mode debug session.
On some targets,
gdbserver supports tracepoints, fast
tracepoints and static tracepoints.
For fast or static tracepoints to work, a special library called the
in-process agent (IPA), must be loaded in the inferior process.
This library is built and distributed as an integral part of
gdbserver. In addition, support for static tracepoints
requires building the in-process agent library with static tracepoints
support. At present, the UST (LTTng Userspace Tracer,
http://lttng.org/ust) tracing engine is supported. This support
is automatically available if UST development headers are found in the
standard include path when
gdbserver is built, or if
gdbserver was explicitly configured using --with-ust
to point at such headers. You can explicitly disable the support
There are several ways to load the in-process agent in your program:
Specifying it as dependency at link time
-linproctraceto the link command.
Using the system's preloading mechanisms
LD_PRELOAD=libinproctrace.soin the environment. See also the description of
gdbserver's --wrapper command line option.
to force loading the agent at run time
dlopen. You'll use the
callcommand for that. For example:
(gdb) call dlopen ("libinproctrace.so", ...)
Note that on most Unix systems, for the
dlopen function to be
available, the program needs to be linked with
On systems that have a userspace dynamic loader, like most Unix
systems, when you connect to
remote, you'll find that the program is stopped at the dynamic
loader's entry point, and no shared library has been loaded in the
program's address space yet, including the in-process agent. In that
case, before being able to use any of the fast or static tracepoints
features, you need to let the loader run and load the shared
libraries. The simplest way to do that is to run the program to the
main procedure. E.g., if debugging a C or C++ program, start
gdbserver like so:
$ gdbserver :9999 myprogram
Start GDB and connect to
gdbserver like so, and run to main:
$ gdb myprogram (gdb) target remote myhost:9999 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2 (gdb) b main (gdb) continue
The in-process tracing agent library should now be loaded into the
process; you can confirm it with the
command, which will list libinproctrace.so as loaded in the
process. You are now ready to install fast tracepoints, list static
tracepoint markers, probe static tracepoints markers, and start
 If you choose a port number that
conflicts with another service,
gdbserver prints an error message