To merge the standard out and standard error streams from a program, use
umount /adsf/asdf 2>&1 will output the errors into standard out instead of standard error as usual.
- 2 is the file descriptor for stderr.
- 1 is the file descriptor for stdout.
- & accepts a file descriptor which can then be treated as a file.
2>&1 in turns ‘writes data’ from stderr into stdout.