Some Answers:
- A non-zero value
- A non-zero value in the ranges 1 through 127 and 138 through 255
- A non-zero value in the ranges 1 through 63, 79 through 127, and 138 through 255
The first answer is certainly correct.
The remaining answers are really a matter of personal preference.
Exit codes 128 through 137:
If a process is terminated by a signal then the standard behaviour is to take the numeric value of the signal, add 128, and use that value as exit code.
128+SIGNAL
So kill -9 someprocess should in theory see the process exit with code 137
There are more than 9 signal codes so you could, if you wish, avoid some of the codes 138 onwards to be absolutely sure.
( Avoiding 128 through 159 might be your preference )
The signal codes for Linux are described here.
Exit codes 64 through 78:
From the Linux exit manpage at kernel.org:
BSD has attempted to standardize exit codes; see the file <sysexits.h>
- EX_USAGE (64) The command was used incorrectly, e.g., with the wrong number of arguments, a bad flag, a bad syntax in a parameter, or whatever.
- EX_CONFIG (78) Something was found in an unconfigured or misconfigured state.
Shell script return codes - my personal suggestion:
Have a quick look through the OpenBSD range 64 to 78 and find something suitable. Then add 100 to that code.
First Example (code 175):
75 in OpenBSD says:
Temporary failure, indicating something that is not really an error. In sendmail, this means that a mailer (e.g.) could not create a connection, and the request should be reattempted later.
( Now adding 100 give 175 which I use )
Second Example (code 178):
78 in OpenBSD says:
Something was found in an unconfigured or misconfigured state.
( Now adding 100 gives 178 which I use )
The bash scripting guide notes (tldp.org):
Appendix D gives some guidance about exit codes.
Linux documentation of sysexits.h (permission of BSD):
#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 */
If you have the Linux source installed then the file
/usr/include/sysexits.h contains the text pasted above.
