gdb(1)

NAME

   gdb - The GNU Debugger

SYNOPSIS

   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

   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@t{++}, 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".  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
           gdb -p 1234

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

   -help
   -h  List all options, with brief explanations.

   -symbols=file
   -s file
       Read symbol table from file file.

   -write
       Enable writing into executable and core files.

   -exec=file
   -e file
       Use file 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 file and use it as the executable file.

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

   -command=file
   -x file
       Execute GDB commands from file file.

   -ex command
       Execute given GDB command.

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

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

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

   -quiet
   -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.

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

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

   -tty=device
       Run using device for your program's standard input and output.

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.

COPYRIGHT

   Copyright (c) 1988-2016 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."

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