Craig Mayhew's Blog » Ubuntu

Chroot in Ubuntu

Craig Mayhew — Tue, 30 Mar 2010 06:43:17 +0000

If you ever manage to damage your ubuntu install so badly that it won’t boot (as I recently did when trying to remove the gnome GUI) then boot from a LiveCD and then open up a terminal.

Type the following commands:

change to the media directory (where our drives should be)
# cd /media

Create a new directory called Ubuntu (We will use this to mount our boot drive too)
# mkdir ubuntu

Mount the boot drive, you will need to replace X with the correct letter
# mount /dev/sdaX /media/ubuntu

Mount some other required locations
# mount –bind /proc /media/ubuntu/proc
# mount –bind /dev /media/ubuntu/dev
# mount –bind /dev/pts /media/ubuntu/dev/pts

Run chroot, using this command and we are now root as if we had booted from the boot drive and not the liveCD:
# chroot /media/ubuntu

Your now in your Ubuntu system as root. If your unsure precisely why your system won’t boot then running an update is usually a good place to start. Good luck!
# aptitude update

The package vmware-server needs to be reinstalled, but I can’t find an archive for it

Craig Mayhew — Mon, 29 Mar 2010 07:00:14 +0000

I recently tried installing a .deb packagae I had made by converting an rpm. Synaptic package manager however errored and since then won’t open. Every time I started synaptic I was getting this error:

The package vmware-server needs to be reinstalled, but I can’t find an archive for it

This command solved it and will force the removal of my incosistent package:

dpkg --remove --force-remove-reinstreq vmware-server

Retrieve Drive UUIDs in Ubuntu

Craig Mayhew — Sat, 27 Mar 2010 14:20:48 +0000

One easy command to retrieve all drive UUIDs.

ls -lF /dev/disk/by-uuid

Greasemonkey scripts won’t update on Ubuntu

Craig Mayhew — Sun, 07 Feb 2010 20:11:00 +0000

The usual reason for not being able to update the scripts is that your permissions are wrong in your Firefox folder. Your Grease Monkey scripts will be in your firefox folder. The default place for this is (please substitute {username} for your actual Ubuntu user name):

cd /home/{username}/.mozilla/firefox/gm_scripts/

You need to make sure you are the owner of this folder. This command will make sure you are. Again please substitute whats inside the {} brackets.

chown -R {username}:{usergroup} /home/{username}/.mozilla/firefox/gm_scripts

If that still fails to fix the problem, then you also need to make sure you have write permissions on your firefox settings folder.

chmod -R 755 /home/{username}/.mozilla/firefox/gm_scripts

ZFS on Ubuntu

Craig Mayhew — Tue, 24 Nov 2009 23:03:23 +0000

Installation on Ubuntu 9.04

Filip Brcic is kindly providing Ubuntu packages for zfs-fuse.

To install zfs-fuse add the Filip Brcic’s launchpad repo to a source list.

sudo nano /etc/apt/sources.list.d/zfs-fuse.list

Add…
At the time of writing, the karmic version of this doesn’t work so keep the word jaunty in repositories and it should be ok.

deb http://ppa.launchpad.net/brcha/ubuntu jaunty main
deb-src http://ppa.launchpad.net/brcha/ubuntu jaunty main

Then update apt.

sudo apt-get update

Now install zfs-fuse.

sudo apt-get install zfs-fuse

CAVEATS:
if you get this message then you need to run the command as root:
connect: Permission denied
internal error: failed to initialize ZFS library

zfs get compressratio

Further Reading:
https://wiki.ubuntu.com/ZFS
https://wiki.ubuntu.com/ZFS/ZPool
http://www.lildude.co.uk/zfs-cheatsheet/
http://blogs.sun.com/bonwick/entry/zfs_dedup

Tell Ubuntu to avoid using SWAP partition with swappiness setting

Craig Mayhew — Wed, 14 Oct 2009 07:00:53 +0000

By Default Ubuntu will move data in RAM onto the swap file/partition on the hard disk long before it runs out of memory. It will pick data that isn’t accessed often but this can still be an annoying slow down on the system. To prevent the over use of SWAP space and speed things up all we need to do is change one setting… swappiness.

Swappiness can be set from 0 to 100. The default is 60 and the lower it is the more the computer will try to keep everything in RAM.

If you want to temporarily change the swappiness then run this command with desired swappiness level:

sudo sysctl vm.swappiness=10

Alternatively if you want the change to be permanent then edit this file:

sudo gedit /etc/sysctl.conf

Set swappiness to the desired level (in this case 1) by either modifying this line in the file “/etc/sysctl.conf” or if it doesn’t exist, add it at the end.

vm.swappiness=1

Reboot the computer for the change to take effect.

Ubuntu Slow Boot: “ata8: SRST failed (error:-16)”

Craig Mayhew — Tue, 29 Sep 2009 07:00:24 +0000

Ubuntu has started being a little slow to boot, as it turns out one of the drives was the cause of this. During the boot up processes ubuntu would hang for a while and then spit out the following: “ata8: SRST failed (error:-16)”. It seems one of my drives wasn’t responding properly during boot up.

To fix this I tried:

- Disabling floppy drive in bios (This didn’t help, but I’m sure it will speed things up slightly as I don’t have a floppy drive)
- Set the “IDE detect time out (sec)” to 0. It was originally 35. (This didn’t help. Be careful when changing this option if you are using IDE drives)
- Unplugged the SATA cable from my DVD drive and plugged it back in again. (PROBLEM SOLVED!)

I imagine either my sata cable is slightly loose or dodgy and reseating it has sorted the problem. If the problem occurs again then I will replace the cable.

“Cannot find or run the base session script. Running Gnome in failsafe session instead.”

Craig Mayhew — Mon, 28 Sep 2009 07:00:28 +0000

After logging into my Ubuntu 9.04 machine I’m greeted with the following message “Cannot find or run the base session script. Running Gnome in failsafe session instead”. The reason for this was I had messed up my permissions and the following fixed it:

After logging in and recieving the errors message press Ctrl-Alt-F1 to drop back into command line. Then run the following:

Sudo chmod 755 /etc/gdm/Xsession

Ubuntu Error “sudo: /etc/sudoers is mode 0640, should be 0440″

Craig Mayhew — Sun, 27 Sep 2009 07:30:03 +0000

If for whatever reason you change the permissions on your sudoers file you will get a similar error to “sudo: /etc/sudoers is mode 0640, should be 0440″ whenever you try to run the sudo command. The problem is that because the permissions are wrong on the sudoers file, linux won’t let you run the sudo command!

To get around this press “Esc” at the grub loader screen when linux is booting and enter into the latest recovery mode. Then select the option that allows you to drop into a command line as root and type

chmod 0440 /etc/sudoers

Then reboot and your troubles should be solved!

Command to find the 10 largest files in linux

Craig Mayhew — Sun, 26 Apr 2009 08:44:58 +0000

The following command will list the top 10 largest files in your linux file system. I’ve confirmed it works on OpenSUSE and Ubuntu 8.04. Remember to run this command as root if you want to search the entire file system.

find / 2>/dev/null -type f -ls | sort -k 7 -r -n | head -10