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gdb(1)




GDB(1)                GNU Development Tools                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:

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

     o   Make your program stop on specified conditions.

     o   Examine  what  has  happened,  when  your  program   has
         stopped.

     o   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:

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GDB(1)                GNU Development Tools                GDB(1)

             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

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GDB(1)                GNU Development Tools                GDB(1)

     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

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     -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

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GDB(1)                GNU Development Tools                GDB(1)

     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) 1988-2018 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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