Linux Commands Examples

A great documentation place for Linux commands


The GNU Debugger



[-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-x file] [-ex cmd] [-d dir] [prog [core|procID]]


[options] --args prog [arguments]



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gdb ./DarwinStreamingServer -x gdb_script
gdb -command "ews_init.gdb" bootimg;

GDB debugging tool for linux

First of all if you don't have a core dumped on your disk is because often by default the core size is limited to 0 byte, thus core are not dumped.

To check this and correct it, simply perform this in your shell just before running your program (in the same shell):

ulimit -c
ulimit -c unlimited

The first command will give you the limit size for core files, the second one will make it unlimited.

Now you can run your program and it will dump a core upon segmentation fault. You still need GDB though.

GDB is an installable package that come with the Red Hat installation DVDs. Red Hat offers a nice and simple interface to do this, check their online manual. Search for GDB, selct it and click Apply. It will request to insert the installation DVD.


sending one key stroke to two windows (Ubuntu)

I don't see an easy way to do this while inside one of your debugging windows, but you could use a third windows running a script that wrapped around xvkbd. It's in the ubuntu repository (might be in universe). The script could read your keyboard input and then call xvkbd twice, sending the keystrokes to both windows. Normally a graphical program, using

xvkbd -window xterm2 -text $foo

sends key events to specific windows, but doesn't invoke a UI. You also might find that wmctrl helps identify windows & stuff. A simplistic script might be:


while [ 1 ]; do
    wmctrl -i -a 0x02200003   #forcibly set focus in window running script
    read keys
    xvkbd -window 0x2202ea4 -text "$keys\r"
    xvkbd -window 0x2200084 -text "$keys\r"

Why gdb is bind to fixed version of autoconf?

Not specific to gdb, an explanation (along with possible solutions) is here.


How to know if gdb is installed?



gdb -help

If GDB is installed then it will display all the available options within your GDB.


The purpose of a debugger such as GDB is to allow you to see what is going on ’’inside’’ another program while it executes—or what another program was doing at the moment it crashed.

GDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:


Start your program, specifying anything that might affect its behavior.


Make your program stop on specified conditions.


Examine what has happened, when your program has stopped.


Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

You can use GDB to debug programs written in C, C++, and Modula-2. Fortran support will be added when a GNU Fortran compiler is ready.

GDB is invoked with the shell command gdb. Once started, it reads commands from the terminal until you tell it to exit with the GDB command quit. You can get online help from gdb itself by using the command help.

You can run gdb with no arguments or options; but the most usual way to start GDB is with one argument or two, specifying an executable program as the argument:

gdb program

You can also start with both an executable program and a core file specified:

gdb program core

You can, instead, specify a process ID as a second argument, if you want to debug a running process:

gdb program 1234

would attach GDB to process 1234 (unless you also have a file named ’1234’; GDB does check for a core file first).

Here are some of the most frequently needed GDB commands:

Set a breakpoint at function (in file).

run [arglist]

Start your program (with arglist, if specified).


Backtrace: display the program stack.

print expr

Display the value of an expression.


Continue running your program (after stopping, e.g. at a breakpoint).


Execute next program line (after stopping); step over any function calls in the line.

edit [file:]function

look at the program line where it is presently stopped.

list [file:]function

type the text of the program in the vicinity of where it is presently stopped.


Execute next program line (after stopping); step into any function calls in the line.

help [name]

Show information about GDB command name, or general information about using GDB.


Exit from GDB.

For full details on GDB, see Using GDB: A Guide to the GNU Source-Level Debugger, by Richard M. Stallman and Roland H. Pesch. The same text is available online as the gdb entry in the info program.


Any arguments other than options specify an executable file and core file (or process ID); that is, the first argument encountered with no associated option flag is equivalent to a ’-se’ option, and the second, if any, is equivalent to a ’-c’ option if it’s the name of a file. Many options have both long and short forms; both are shown here. The long forms are also recognized if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with ’+’ rather than ’-’, though we illustrate the more usual convention.)

All the options and command line arguments you give are processed in sequential order. The order makes a difference when the ’-x’ option is used.



List all options, with brief explanations.


Read symbol table from file file.


Enable writing into executable and core files.


Use file file as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump.


Read symbol table from file file and use it as the executable file.


Use file file as a core dump to examine.


Execute GDB commands from file file.

-ex command

Execute given GDB command.


Add directory to the path to search for source files.


Do not execute commands from ~/.gdbinit.



Do not execute commands from any ’.gdbinit’ initialization files.



’’Quiet’’. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.


Run in batch mode. Exit with status 0 after processing all the command files specified with ’-x’ (and ’.gdbinit’, if not inhibited). Exit with nonzero status if an error occurs in executing the GDB commands in the command files.

Batch mode may be useful for running GDB as a filter, for example to download and run a program on another computer; in order to make this more useful, the message

Program exited normally.

(which is ordinarily issued whenever a program running under GDB control terminates) is not issued when running in batch mode.


Run GDB using directory as its working directory, instead of the current directory.



Emacs sets this option when it runs GDB as a subprocess. It tells GDB to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time the program stops). This recognizable format looks like two ’ 32’ characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-GDB interface program uses the two ’ 32’ characters as a signal to display the source code for the frame.

-b bps

Set the line speed (baud rate or bits per second) of any serial interface used by GDB for remote debugging.


Run using device for your program’s standard input and output.


Pass arguments after the program name to the program when it is run.


Run GDB using a text (console) user interface.


Copyright (c) 1991, 2010 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be included in translations approved by the Free Software Foundation instead of in the original English.

see also

The full documentation for gdb is maintained as a Texinfo manual. If the info and gdb programs and GDB’s Texinfo documentation are properly installed at your site, the command

info gdb

should give you access to the complete manual.

Using GDB: A Guide to the GNU Source-Level Debugger, Richard M. Stallman and Roland H. Pesch, July 1991.

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