EX_USAGE

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 remote logins.

The host specified did not exist. This is used in mail addresses or network requests.

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. For example that a mailer 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_NOINPUT or EX_CANTCREAT, but rather for higher level permissions.

Something was found in an unconfigured or misconfigured state.