| 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_DATAERR(65) | The input data was incorrect in some way. This should only be used for user’s data and not system files. |
| EX_NOINPUT(66) | 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). |
| EX_NOUSER(67) | The user specified did not exist. This might be used for mail addresses or remote logins. |
| EX_NOHOST(68) | The host specified did not exist. This is used in mail addresses or network requests. |
| EX_UNAVAILABLE(69) | A service is unavailable. This can occur if a support program or file does not exist. This can also be used as a catchall message when something you wanted to do does not work, but you do not know why. |
| EX_SOFTWARE(70) | An internal software error has been detected. This should be limited to non-operating system related errors as possible. |
| EX_OSERR(71) | An operating system error has been detected. This is intended to be used for such things as "cannot fork", "cannot create pipe", or the like. It includes things like getuid returning a user that does not exist in the passwd file. |
| EX_OSFILE(72) | Some system file (e.g., /etc/passwd, /var/run/utmp, etc.) does not exist, cannot be opened, or has some sort of error (e.g., syntax error). |
| EX_CANTCREAT(73) | A (user specified) output file cannot be created. |
| EX_IOERR(74) | An error occurred while doing I/O on some file. |
| EX_TEMPFAIL(75) | 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. |
| EX_PROTOCOL(76) | The remote system returned something that was "not possible" during a protocol exchange. |
| EX_NOPERM(77) | You did not have sufficient permission to perform the operation. This is not intended for file system problems, which should use EX_NOINPUT or EX_CANTCREAT, but rather for higher level permissions. |
| EX_CONFIG(78) | Something was found in an unconfigured or misconfigured state. |
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