Are there any standard exit status codes in Linux

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A process is considered to have completed correctly in Linux if its exit status was 0   I ve seen that segmentation faults often result in an exit status of 11  though I don t know if this is simply the convention where I work  the apps that failed like that have all been internal  or a standard   Are there standard exit codes for processes in Linux

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Part 1  Advanced Bash Scripting Guide  As always  the Advanced Bash Scripting Guide has great information    This was linked in another answer  but to a non-canonical URL       1   Catchall for general errors   2  Misuse of shell builtins  according to Bash documentation    126   Command invoked cannot execute   127    command not found    128   Invalid argument to exit   128 n   Fatal error signal  n    255  Exit status out of range  exit takes only integer args in the range 0 - 255    Part 2  sysexits h  The ABSG references sysexits h   On Linux     find  usr -name sysexits h  usr include sysexits h   cat  usr include sysexits h        Copyright  c  1987  1993     The Regents of the University of California   All rights reserved     A whole bunch of text left out     define EX OK           0          successful termination     define EX  BASE        64         base value for error messages     define EX USAGE        64         command line usage error     define EX DATAERR      65         data format error     define EX NOINPUT      66         cannot open input         define EX NOUSER       67         addressee unknown         define EX NOHOST       68         host name unknown     define EX UNAVAILABLE  69         service unavailable     define EX SOFTWARE     70         internal software error     define EX OSERR        71         system error  e g   can t fork      define EX OSFILE       72         critical OS file missing     define EX CANTCREAT    73         can t create  user  output file     define EX IOERR        74         input output error     define EX TEMPFAIL     75         temp failure  user is invited to retry     define EX PROTOCOL     76         remote error in protocol     define EX NOPERM       77         permission denied     define EX CONFIG       78         configuration error      define EX  MAX 78         maximum listed value

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1      Catchall for general errors   2      Misuse of shell builtins  according to Bash documentation    126     Command invoked cannot execute   127     command not found     128     Invalid argument to exit   128 n    Fatal error signal  n        130     Script terminated by Control-C    255    Exit status out of range  This is for bash  However  for other applications  there are different exit codes

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None of the older answers describe exit status 2 correctly  Contrary to what they claim  status 2 is what your command line utilities actually return when called improperly   Yes  an answer can be nine years old  have hundreds of upvotes  and still be wrong    Here is the real  long-standing exit status convention for normal termination  i e  not by signal    Exit status 0  success Exit status 1   failure   as defined by the program Exit status 2  command line usage error   For example  diff returns 0 if the files it compares are identical  and 1 if they differ  By long-standing convention  unix programs return exit status 2 when called incorrectly  unknown options  wrong number of arguments  etc    For example  diff -N  grep -Y or diff a b c will all result in    being set to 2  This is and has been the practice since the early days of Unix in the 1970s   The accepted answer explains what happens when a command is terminated by a signal  In brief  termination due to an uncaught signal results in exit status 128   lt signal number gt   E g   termination by SIGINT  signal 2  results in exit status 130    Notes   Several answers define exit status 2 as  Misuse of bash builtins   This applies only when bash  or a bash script  exits with status 2  Consider it a special case of incorrect usage error  In sysexits h  mentioned in the most popular answer  exit status EX USAGE   command line usage error   is defined to be 64  But this does not reflect reality  I am not aware of any common Unix utility that returns 64 on incorrect invocation  examples welcome   Careful reading of the source code reveals that sysexits h is aspirational  rather than a reflection of true usage           This include file attempts to categorize possible error       exit statuses for system programs  notably delivermail       and the Berkeley network         Error numbers begin at EX  BASE  64  to reduce the possibility of        clashing with oth  er exit statuses that random programs may        already return      In other words  these definitions do not reflect the common practice at the time  1993  but were intentionally incompatible with it  More s the pity

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There are no standard exit codes  aside from 0 meaning success  Non-zero doesn t necessarily mean failure either   stdlib h does define EXIT FAILURE as 1 and EXIT SUCCESS as 0  but that s about it   The 11 on segfault is interesting  as 11 is the signal number that the kernel uses to kill the process in the event of a segfault  There is likely some mechanism  either in the kernel or in the shell  that translates that into the exit code

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sysexits h has a list of standard exit codes  It seems to date back to at least 1993 and some big projects like Postfix use it  so I imagine it s the way to go   From the OpenBSD man page    According to style 9   it is not good practice to call exit 3  with arbi- trary values to indicate a failure condition when ending a program   In- stead  the pre-defined exit codes from sysexits should be used  so the caller of the process can get a rough estimation about the failure class without looking up the source code

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When Linux returns 0  it means success   Anything else means failure  each program has its own exit codes  so it would been quite long to list them all       About the 11 error code  it s indeed the segmentation fault number  mostly meaning that the program accessed a memory location that was not assigned

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8 bits of the return code and 8 bits of the number of the killing signal are mixed into a single value on the return from wait 2   amp  co     include  lt stdio h gt   include  lt stdlib h gt   include  lt sys types h gt   include  lt sys wait h gt   include  lt unistd h gt   include  lt signal h gt   int main         int status       pid t child   fork        if  child  lt   0          exit 42       waitpid child   amp status  0       if  WIFEXITED status           printf  first child exited with  u n   WEXITSTATUS status           prints   first child exited with 42          child   fork        if  child  lt   0          kill getpid    SIGSEGV       waitpid child   amp status  0       if  WIFSIGNALED status           printf  second child died with  u n   WTERMSIG status           prints   second child died with 11         How are you determining the exit status   Traditionally  the shell only stores an 8-bit return code  but sets the high bit if the process was abnormally terminated      sh -c  exit 42   echo    42   sh -c  kill -SEGV      echo    Segmentation fault 139   expr 139 - 128 11   If you re seeing anything other than this  then the program probably has a SIGSEGV signal handler which then calls exit normally  so it isn t actually getting killed by the signal    Programs can chose to handle any signals aside from SIGKILL and SIGSTOP

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Standard Unix exit codes are defined by sysexits h  as another poster mentioned  The same exit codes are used by portable libraries such as Poco - here is a list of them   http   pocoproject org docs Poco Util Application html 16218  A signal 11 is a SIGSEGV  segment violation  signal  which is different from a return code  This signal is generated by the kernel in response to a bad page access  which causes the program to terminate  A list of signals can be found in the signal man page  run  man signal

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To a first approximation  0 is success  non-zero is failure  with 1 being general failure  and anything larger than one being a specific failure   Aside from the trivial exceptions of false and test  which are both designed to give 1 for success  there s a few other exceptions I found  More realistically  0 means success or maybe failure   1 means general failure or maybe success  2 means general failure if 1 and 0 are both used for success  but maybe sucess as well  The diff command gives 0 if files compared are identical  1 if they differ  and 2 if binaries are different  2 also means failure   The less command gives 1 for failure unless you fail to supply an argument  in which case  it exits 0 despite failing  The more command and the spell command give 1 for failure  unless the failure is a result of permission denied  nonexistent file  or attempt to read a directory   In any of these cases  they exit 0 despite failing  Then the expr command gives 1 for success unless the output is the empty string or zero  in which case  0 is success   2 and 3 are failure  Then there s cases where success or failure is ambiguous   When grep fails to find a pattern  it exits 1  but it exits 2 for a genuine failure  like permission denied    Klist also exits 1 when it fails to find a ticket  although this isn t really any more of a failure than when grep doesn t find a pattern  or when you ls an empty directory  So  unfortunately  the unix powers that be don t seem to enforce any logical set of rules  even on very commonly used executables

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Programs return a 16 bit exit code   If the program was killed with a signal then the high order byte contains the signal used  otherwise the low order byte is the exit status returned by the programmer   How that exit code is assigned to the status variable    is then up to the shell   Bash keeps the lower 7 bits of the status and then uses 128    signal nr  for indicating a signal   The only  standard  convention for programs is 0 for success  non-zero for error   Another convention used is to return errno on error

[linux] Are there any standard exit status codes in Linux?

Part 1: Advanced Bash Scripting Guide

Part 2: sysexits.h

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