GDB linux command manual

gdb(1)                                GNU Tools                            gdb(1)

       gdb - The GNU Debugger

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

       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 cor-
              recting the effects of  one  bug  and  go  on  to  learn  about

       You  can  use  GDB  to debug programs written in C, C++, and Modula-2.
       Fortran support will be added when a GNU Fortran compiler is ready.

       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 com-
       mand quit.  You can get online help from gdb itself by using the  com-
       mand 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,  if  you
       want to debug a running process:

       gdb program 1234

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

       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 break-

       next   Execute next program line (after stopping); step over any func-
              tion 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 func-
              tion 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.

       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 sec-
       ond, 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.


       -h     List all options, with brief explanations.


       -s file
               Read symbol table from file file.

       -write Enable writing into executable and core files.


       -e file
               Use file file as the executable file to execute when appropri-
              ate, and for examining pure data in  conjunction  with  a  core

                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.


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


       -n     Do not execute  commands  from  any  '.gdbinit'  initialization
              files.   Normally,  the  commands  in  these files are executed
              after all the command options  and  arguments  have  been  pro-


       -q     ''Quiet''.   Do  not  print the introductory and copyright mes-
              sages.  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 exam-
              ple 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

                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  dis-
              played (which includes each time the program stops).  This rec-
              ognizable format looks like two ' 32' 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 ' 32' 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.

       'gdb' entry in info; Using GDB: A Guide to the GNU Source-Level Debug-
       ger, Richard M. Stallman and Roland H. Pesch, July 1991.

       Copyright (c) 1991 Free Software Foundation, Inc.

       Permission  is  granted to make and distribute verbatim copies of this
       manual provided the copyright notice and this  permission  notice  are
       preserved on all copies.

       Permission is granted to copy and distribute modified versions of this
       manual under the conditions for verbatim copying,  provided  that  the
       entire resulting derived work is distributed under the terms of a per-
       mission notice identical to this one.

       Permission is granted to copy and distribute translations of this man-
       ual  into  another  language,  under the above conditions for modified
       versions, except that this permission notice may be included in trans-
       lations  approved  by  the  Free Software Foundation instead of in the
       original English.

GNU Tools                         22may2002                            gdb(1)