Ubuntu Manpage: gdb - The GNU Debugger

NAME

       gdb - The GNU Debugger

SYNOPSIS

       gdb [OPTIONS] [prog|prog procID|prog core]

DESCRIPTION

       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.

OPTIONS

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 supressed
(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.

COPYRIGHT

       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."

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

SEE ALSO

COPYRIGHT