preferable exit codes for programs
It is not good practice to call
with arbitrary values to
indicate a failure condition when ending a program. Instead, the pre-defined
exit codes from
should be used, so the caller
of the process can get a rough estimation about the failure class without
looking up the source code.
The successful exit is always indicated by a status of 0, or
EX_OK. Error numbers begin at
EX__BASE to reduce the possibility of clashing with
other exit statuses that random programs may already return. The meaning of
the code is approximately as follows:
- The command was used incorrectly, e.g., with the wrong number of
arguments, a bad flag, bad syntax in a parameter, or whatever.
- The input data was incorrect in some way. This should only be used for
user's data and not system files.
- An input file (not a system file) did not exist or was not readable. This
could also include errors like “No message” to a mailer (if
it cared to catch it).
- The user specified did not exist. This might be used for mail addresses or
- The host specified did not exist. This is used in mail addresses or
- A service is unavailable. This can occur if a support program or file does
not exist. This can also be used as a catch-all message when something you
wanted to do doesn't work, but you don't know why.
- An internal software error has been detected. This should be limited to
non-operating system related errors if possible.
- An operating system error has been detected. This is intended to be used
for such things as “cannot fork”, or “cannot create
pipe”. It includes things like
getuid(2) returning a user
that does not exist in the passwd file.
- Some system file (e.g., /etc/passwd,
/var/run/utmp) does not exist, cannot be opened,
or has some sort of error (e.g., syntax error).
- A (user specified) output file cannot be created.
- An error occurred while doing I/O on some file.
- Temporary failure, indicating something that is not really an error. In
sendmail, this means that a mailer, for example, could not create a
connection, and the request should be reattempted later.
- The remote system returned something that was “not possible”
during a protocol exchange.
- You did not have sufficient permission to perform the operation. This is
not intended for file system problems, which should use
EX_CANTCREAT, but rather for higher level
- Something was found in an unconfigured or misconfigured state.
The numerical values corresponding to the symbolical ones are
given in parentheses for easy reference.
file first appeared in
for use by the delivermail utility, later
renamed to sendmail(8)
file in 1980. This man page was written by
, based on Eric's original comments found
The choice of an appropriate exit value is often ambiguous.