Once, I was going to make a quick backup copy of /usr on a busy multi-user system. I did:
$ (cd /usr; tar cf - *) | (cd /mnt; tar xvpf -)
Only I typoed ’cd /mnt’ which made the changedir fail and my current working dir was /usr so I had one tar-process archiving /usr then streaming the data to another tar process that used it to overwrite everything under /usr. After a few seconds of nothing appearing under /mnt I got really nervous I’d done something stupid. Then I realised what was happening and had a couple more seconds of hoping it’d be fine (given that I was overwriting /usr with its own data). Then the system log lit up like a christmas tree with error messages and a few seconds later the machine froze. Can’t recommend doing backups this way.
$ (cd /usr; tar cf - *) | (cd /mnt; tar xvpf -)
Only I typoed ’cd /mnt’ which made the changedir fail and my current working dir was /usr so I had one tar-process archiving /usr then streaming the data to another tar process that used it to overwrite everything under /usr. After a few seconds of nothing appearing under /mnt I got really nervous I’d done something stupid. Then I realised what was happening and had a couple more seconds of hoping it’d be fine (given that I was overwriting /usr with its own data). Then the system log lit up like a christmas tree with error messages and a few seconds later the machine froze. Can’t recommend doing backups this way.