Troubleshooting (Ubuntu)
For performance problems related load, see High System Load
Network
No NIC
Especially after hardware changes, its possible the networking config no longer refers to the right interface.
- Use
ifconfig
to confirm the current network config - Use
dmesg | grep -i eth
to ascertain what's been detected at boot time - Assuming it states that say
eth0
has been changed toeth1
then just update the/etc/network/interfaces
file - Alternatively, force the new NIC to be
eth0
by editing the/etc/udev/rules.d/70-persistent-net.rules
file- You'll need to reboot the server for changes to take effect
File System
Unable to Mount CD-ROM
Mounting drive with following command fails
mount /dev/cdrom /media/cdrom/
If /media/cdrom/
doesn't exist
- Create the file with
mkdir /media/cdrom
If /dev/cdrom
special device doesn't exist
- Check for existing mappings and devices
ls -l /dev/ | grep cdrom
- If an existing mapping exists but for a different drive number (eg
cdrom2 -> sr0
)- Then try mounting with that number
- EG
mount /dev/cdrom2 /media/cdrom/
- If no existing mapping exists
- Then try creating one for one of the listed devices
- EG
ln -sf /dev/sg0 /dev/cdrom
Replacing a Software RAID 1 Disk
This procedure was written from the following starting point...
- A machine originally with two disks in RAID1 has failed, one disk has been replaced, and machine started again
...and adapted from this post http://www.howtoforge.com/replacing_hard_disks_in_a_raid1_array
- Backup whatever you can before proceeding, one mistake or system error could destroy your machine
- Confirm which disk is new, and which is old (if the new disk is blank this is easy as there will be no partition info!)
fdisk -l
- Partition the new disk the same as the original
sfdisk -d /dev/sda | sfdisk /dev/sdb
- Confirm that the layout of both disks is now that same
fdisk -l
- Add the newly created partitions to the RAID disks
mdadm --manage /dev/md0 --add /dev/sdb1
- You may have more
sd
partitions thanmd
partitions, the array size return throughmdadm -D /dev/md*
should roughly match the number of blocks found fromfdisk -l
- The arrays should now be being sync'ed, check progress by monitoring
/proc/mdstat
more /proc/mdstat
Recover Deleted Files
Ideally you should recover files to a seperate disk partition to the one you are attempting to recover from. This procedure should help to recover lost or corrupted files from a filesystem using Scalpel, a data recovery utility built on the foundation of Foremost
- Install Scalpel
apt-get install scalpel
- Update the config file to search for the lost files (uncomment/add as neccessary)
/etc/scalpel/scalpel.conf
- For PHP files (not embedded in HTML) use
php n 50000 <?php ?>
- Create a folder for the recovered files to go to
mkdir /tmp/recov
- Launch Scalpel to trawl the disk image (will takes ages, and source disk will be under high load)
scalpel /dev/mapper/svr-root -o /tmp/recov/
- Search through recovered files to find the data of interest
grep -R "string you want to find" /tmp/recov/*
SSH
Server Hostname Change
If the hostname (or IP) of the server you are SSH'ing to changes, the old entry needs to be removed from your SSH key known hosts file
ssh-keygen -R <name or IP>
Packages
Errors etc received from apt-get
- Error 400 Bad Request
- Somewhat misleadingly, the problem is normal caused by being unable to contact the update server. Consider adding proxy server config to your machine
- The following packages have been kept back
- Package manager can hold back updates because they will cause conflicts, or sometimes because they're major kernel updates. Running
aptitude safe-upgrade
normally seems to force kernel updates through.
- Package manager can hold back updates because they will cause conflicts, or sometimes because they're major kernel updates. Running
Add EOL Repository
Once a version of Ubuntu has gone End Of Line (EOL), you can't install software packages using the normal repository. On trying you'll get an error similar to
Failed to fetch http://gb.archive.ubuntu.com/ubuntu/pool/main/s/<package> 404 Not Found
The repository is still available, but via a different URL - http://old-releases.ubuntu.com
Edit /etc/apt/sources.list
and add the following (replace hardy with your flavour of Ubuntu). Remove the existing ubuntu repositories (they'll just cause errors as they're inaccessible)
# Hardy EOL # Required deb http://old-releases.ubuntu.com/ubuntu/ hardy main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ hardy-updates main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ hardy-security main restricted universe multiverse # Optional #deb http://old-releases.ubuntu.com/ubuntu/ hardy-backports main restricted universe multiverse
Reboot Required?
If a package update/installation requires a reboot to complete the following file will exist...
/var/run/reboot-required
To see which packages caused this to be set, inspect the contents of...
/var/run/reboot-required.pkgs
Firewall
ERROR: problem running ufw-init
If on starting or reloading ufw
you receive this error, its likely that you have a configuration problem. This is especially likely if you've needed to edit ufw
's config files directly.
- Ensure that
ufw
is runningufw enable
- Force the config to be reloaded
/lib/ufw/ufw-init force-reload
- Or if
ufw
failed to start use/lib/ufw/ufw-init start
Doing the above should trigger the error, and present a better description of what the problem is
See http://ubuntuforums.org/showthread.php?t=1660916 for further info