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Restoring the contents of /dev

Have you ever deleted everything out of /dev by accident (or even on purpose)? Although it may seem that all is lost or that you have a lot of work ahead of you, it’s actually quite easy to restore on a modern Linux system such as CentOS 5 (or the RHEL equivalent).

The first thing you need to know is that CentOS and Red Hat use udevd, which means that the entries in /dev are dynamically created by the udev daemon and restarting this daemon will force it to re-create everything in /dev, just as it would when you start your computer up. This daemon isn’t controller in the normal way through the /etc/init.d scripts though, all you need to run is:

/sbin/start_udev

This will kill any copies of udev running and then start it back up, re-creating the /dev entries in the process. This seems to be quite safe to do on a production system, but it might be wise to only do this if you really have to, as if you haven’t damaged the contents of /dev, then some of your applications may not take kindly to the contents disappearing.

This will have re-created most of your device nodes in /dev, but there are still a couple of important ones missing, namely those used by device-mapper and LVM. You can get these back with the following two commands:

dmsetup mknodes
vgmknodes

The first of which will re-create entries under /dev/mapper and the second of which will re-create LVM volume group entries under /dev/ such as /dev/VolGroup00/ by default on CentOS or Red Hat.

Helpfully this will save someone a real headache or even rebuilding/restoring from backup unnecessarily. Just be more careful with rm next time! 😉

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