How to convert errno in UNIX to corresponding string?

strerror() should do it. http://linux.die.net/man/3/strerror

FYI, so that you can find these things more easily, yourself: If you type man errno (or whatever function you're investigating), and look at the very bottom of the man page, you'll see a list of related functions. If you man each of those (taking a guess about which one(s) to do first based on their names) you'll often find the answer to similar questions.

There's now an errno utility distributed with the moreutils package.

$ errno -h
Usage: errno [-lsS] [--list] [--search] [--search-all-locales] [keyword]

$ errno -l
EPERM 1 Operation not permitted
ENOENT 2 No such file or directory
ESRCH 3 No such process
EINTR 4 Interrupted system call
EIO 5 Input/output error
ENXIO 6 No such device or address
E2BIG 7 Argument list too long
ENOEXEC 8 Exec format error
...

$ errno 11
EAGAIN 11 Resource temporarily unavailable

$ errno -s Ouput
EIO 5 Input/output error

Just another solution that solves exactly the problem you have, but in Python instead of C:

>>> import errno
>>> errno.errorcode[errno.EIDRM]
'EIDRM'