Are there any standard exit status codes in Linux?
'1': Catch-all 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 Ctrl + C
'255': Exit status out of range
This is for Bash. However, for other applications, there are different exit codes.
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 */
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)
& co..
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <signal.h>
int main() {
int status;
pid_t child = fork();
if (child <= 0)
exit(42);
waitpid(child, &status, 0);
if (WIFEXITED(status))
printf("first child exited with %u\n", WEXITSTATUS(status));
/* prints: "first child exited with 42" */
child = fork();
if (child <= 0)
kill(getpid(), SIGSEGV);
waitpid(child, &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
.)
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+[<signal number>
. 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 statusEX_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 thatsysexits.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 other 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.