In a document created by a former coworker there is this command:
cat /dev/null > /var/spool/mail/root
It says next to it that it will clean out mailbox.
Can someone please explain how/why these commands do that. I need to know what will happen before I run the command.
We are trying to clean up space on var, as of right now it's at 91%.
The command will output the data from device /dev/null to the given file (mailbox of the root account). Since /dev/null responds just with end-of-file when reading from it nothing will be written to the file, but with the redirection > the shell will have cleared the file already. Actually this is equivalent to writing just
> /var/spool/mail/root
(i.e., the same without cat or /dev/null).
truncate -s 0 /var/spool/mail/root.
– derobert
Mar 11 '15 at 16:40
cat /dev/null > /var/spool/mail/root truncates /var/spool/mail/root
Alternative is > /var/spool/mail/root
/var/spool/mail/root– Milind Dumbare Mar 11 '15 at 15:30