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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SEE ALSO | COPYRIGHT | COLOPHON |
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GDB(1) GNU Development Tools GDB(1)
gdb - The GNU Debugger
gdb [OPTIONS] [prog|prog procID|prog core]
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++, Fortran and
Modula-2.
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" or "exit". 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 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|line]
Set a breakpoint at function or line (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
breakpoint).
next
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.
step
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.
quit
exit
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
abbreviated 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.
The abbreviated forms are shown here with - and long forms are
shown with -- to reflect how they are shown in --help. However,
GDB recognizes all of the following conventions for most options:
"--option=value"
"--option value"
"-option=value"
"-option value"
"--o=value"
"--o value"
"-o=value"
"-o value"
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.
--help
-h List all options, with brief explanations.
--symbols=file
-s file
Read symbol table from file.
--write
Enable writing into executable and core files.
--exec=file
-e file
Use file as the executable file to execute when appropriate,
and for examining pure data in conjunction with a core dump.
--se=file
Read symbol table from file and use it as the executable
file.
--core=file
-c file
Use file as a core dump to examine.
--command=file
-x file
Execute GDB commands from file.
--eval-command=command
-ex command
Execute given GDB command.
--init-eval-command=command
-iex
Execute GDB command before loading the inferior.
--directory=directory
-d directory
Add directory to the path to search for source files.
--nh
Do not execute commands from ~/.config/gdb/gdbinit,
~/.gdbinit, ~/.config/gdb/gdbearlyinit, or ~/.gdbearlyinit
--nx
-n Do not execute commands from any .gdbinit or .gdbearlyinit
initialization files.
--quiet
--silent
-q "Quiet". Do not print the introductory and copyright
messages. These messages are also suppressed in batch mode.
--batch
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.
--batch-silent
Run in batch mode, just like --batch, but totally silent.
All GDB output is suppressed (stderr is unaffected). This is
much quieter than --silent and would be useless for an
interactive session.
This is particularly useful when using targets that give
Loading section messages, for example.
Note that targets that give their output via GDB, as opposed
to writing directly to "stdout", will also be made silent.
--args prog [arglist]
Change interpretation of command line so that arguments
following this option are passed as arguments to the
inferior. As an example, take the following command:
gdb ./a.out -q
It would start GDB with -q, not printing the introductory
message. On the other hand, using:
gdb --args ./a.out -q
starts GDB with the introductory message, and passes the
option to the inferior.
--pid=pid
Attach GDB to an already running program, with the PID pid.
--tui
Open the terminal user interface.
--readnow
Read all symbols from the given symfile on the first access.
--readnever
Do not read symbol files.
--return-child-result
GDB's exit code will be the same as the child's exit code.
--configuration
Print details about GDB configuration and then exit.
--version
Print version information and then exit.
--cd=directory
Run GDB using directory as its working directory, instead of
the current directory.
--data-directory=directory
-D Run GDB using directory as its data directory. The data
directory is where GDB searches for its auxiliary files.
--fullname
-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 baudrate
Set the line speed (baud rate or bits per second) of any
serial interface used by GDB for remote debugging.
-l timeout
Set timeout, in seconds, for remote debugging.
--tty=device
Run using device for your program's standard input and
output.
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 (c) 1988-2023 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."
This page is part of the gdb (GNU debugger) project. Information
about the project can be found at
⟨http://www.gnu.org/software/gdb/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/gdb/bugs/⟩.
This page was obtained from the tarball gdb-14.2.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/gdb/⟩ on 2024-06-14. 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 [email protected]
gdb-14.2 2024-03-03 GDB(1)
Pages that refer to this page: coredumpctl(1), dbpmda(1), pldd(1), pmdbg(1), stap(1), stap-merge(1), ptrace(2), abort(3), backtrace(3), core(5), elf(5), gdbinit(5), proc_pid_maps(5), stappaths(7), crash(8), systemd-coredump(8), systemd-sysext(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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