Q:

How to recover basic networking utilities on Debian?

I am administrating a small server for LAN, providing basic services such as web-proxy, ldap, kerberos, afs, etc. Yesterday there was a power cut so server halted. When I restarted it no network interfaces were available and configured. I tried restarting networking daemon but it just exited with 0 status. So I tried to run one of the interfaces manually, but ifup and ifdown commands simply are not there. No only in PATH, but they disappeared from /sbin.
So my question is: how can I recover these network utilities?

A:

Are there any messages in /var/log/messages, /var/log/syslog, /var/log/boot.log, etc. indicating an I/O error or an error mounting a partition or an error activating LVM or MD or RAID?
Was there a "Filesystem unclean" or "fsck" message when the server powered up?
Are all partitions currently mounted?  Are there any files in /sbin?
To fix the exact problem you mention, assuming all partitions were correctly mounted, I would boot from a Debian boot CD in recovery/rescue mode, start a shell, find where your /sbin (or probably the / (root)) partition is mounted, then run chroot <that path> /bin/bash, then you can run sudo apt-get install ifupdown to re-install /sbin/ifup, then reboot.
But you should try to find out if anything else is broken.  Try installing debsums, i.e. sudo apt-get install debsums.

