gdb(1) — Linux manual page


GDB(1)                      GNU Development Tools                     GDB(1)

NAME         top

       gdb - The GNU Debugger

SYNOPSIS         top

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

DESCRIPTION         top

       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

       •   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

       You can use GDB to debug programs written in C, C++, Fortran and

       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

               gdb program core

       You can, instead, specify a process ID as a second argument or use
       option "-p", if you want to debug a running process:

               gdb program 1234
               gdb -p 1234

       would attach GDB to process 1234.  With option -p you can omit the
       program filename.

       Here are some of the most frequently needed GDB commands:

       break [file:]function
           Set a breakpoint at function (in file).

       run [arglist]
           Start your program (with arglist, if specified).

       bt  Backtrace: display the program stack.

       print expr
           Display the value of an expression.

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

           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.

OPTIONS         top

       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

       -h  List all options, with brief explanations.

       -s file
           Read symbol table from file file.

           Enable writing into executable and core files.

       -e file
           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

       -c file
           Use file file as a core dump to examine.

       -x file
           Execute GDB commands from file file.

       -ex command
           Execute given GDB command.

       -d directory
           Add directory to the path to search for source files.

       -nh Do not execute commands from ~/.gdbinit.

       -n  Do not execute commands from any .gdbinit initialization files.

       -q  "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.

       -f  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 \032 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 \032 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.

SEE ALSO         top

       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.

COPYRIGHT         top

       Copyright (c) 1988-2020 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3 or
       any later version published by the Free Software Foundation; with the
       Invariant Sections being "Free Software" and "Free Software Needs
       Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
       and with the Back-Cover Texts as in (a) below.

       (a) The FSF's Back-Cover Text is: "You are free to copy and modify
       this GNU Manual.  Buying copies from GNU Press supports the FSF in
       developing GNU and promoting software freedom."

COLOPHON         top

       This page is part of the gdb (GNU debugger) project.  Information
       about the project can be found at ⟨⟩.
       If you have a bug report for this manual page, see
       ⟨⟩.  This page was obtained from
       the tarball gdb-10.1.tar.gz fetched from
       ⟨⟩ on 2020-11-01.  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

gdb-10.1                         2020-10-24                           GDB(1)

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