If you tried installing or upgrading Ubuntu recently, you probably noticed that all the storage devices are now using UUID – Universally Unique IDentifiers. I’m not claiming to know everything there is to know about UUIDs, but have become quite comfortable managing them lately, so hopefully this post will help you achieve the same.

What is a UUID exactly?

UUID is a Universally Unique IDentifier. It’s a identification code given to each storage device you have on your system, aimed to help you uniquely identify each device no matter what.

UUIDs can be used to identify DVD drives, removable media (USB flashsticks) and each partition on any of your hard drives.

This is how a typical UUID looks:

c73a37c8-ef7f-40e4-b9de-8b2f81038441

Why use UUID?

Reason 1: Truly unique identification

UUID is the only way to guarantee you recognize the same drive or partition no matter what. For example, if you introduce to your system another hard drive, this might upset quite a few things, starting with the way your system boots up (or stops booting up upon the new drive introduction). Using UUID helps remedy most of such things.

Reason 2: Device names are not always persistent

Automatically assigned device names in your system are not consistent, they are according to the order of loading the kernel modules up during (most usually) the startup time, and thus the names will look different if you boot with one of your USB flashsticks attached and then reboot after you plug it out.

Generally, I’ve also found UUIDs really useful for mounting my removable media – I have a USB reader, one of the 24-in-1 kinds – it supports various types of cards and I use UUID to always mount the same card at the same location.

Reason 3: Most critical functionality of your Ubuntu system already depends on UUIDs

GRUB – your boot loader – relies on UUIDs as well. If you look into /boot/grub/menu.lst file, you’ll find something similar to this:

title Ubuntu hardy (development branch), kernel 2.6.24-16-generic
root (hd2,0)
kernel /boot/vmlinuz-2.6.24-16-generic root=UUID=c73a37c8-ef7f-40e4-b9de-8b2f81038441 ro quiet splash
initrd /boot/initrd.img-2.6.24-16-generic
quiet

List UUIDs for all your devices

If you are using one of the recent releases of Ubuntu (UUIDs have been there since Edgy), you can use the blkid command to get a list of all the drives and partitions along with their UUIDs:

ubuntu# blkid
/dev/sda1: UUID="2220CF8220CF5B83" TYPE="ntfs"
/dev/sda2: UUID="48E81F29E81F14B2" LABEL="DRIVE-D" TYPE="ntfs"
/dev/sdb1: UUID="c73a37c8-ef7f-40e4-b9de-8b2f81038441" SEC_TYPE="ext2" TYPE="ext3"
/dev/sdb5: TYPE="swap" UUID="abe7529e-dcd5-4afc-b714-05569dbcd30b"
/dev/sdb6: UUID="f34c8c7c-a020-4a14-8c97-257180240250" SEC_TYPE="ext2" TYPE="ext3"
/dev/sdb7: UUID="8fa274ca-5b22-411f-b5da-7469c1f276da" SEC_TYPE="ext2" TYPE="ext3"
/dev/sdc1: UUID="1e36f323-c4e5-4f55-ba0a-838643550bf9" TYPE="ext3" SEC_TYPE="ext2"
/dev/sdc2: UUID="83aa92e4-4df4-4aab-80f3-9bbb447e0459" TYPE="ext3" SEC_TYPE="ext2"

As you can see, I’ve still got a few NTFS partitions as I’m slowly migrating my data from Windows after my switch to Ubuntu desktop a couple months ago.

Get UUID for a particular device

If you know a device name and just want to confirm the UUID for it to later use it in /etc/fstab, here’s how you can do it using vol_id command:

ubuntu# vol_id -u /dev/sdb1
c73a37c8-ef7f-40e4-b9de-8b2f81038441

That’s all I can think of so far. I know a few more things about UUID which I’ll share in a separate post, but it’s a start.

Have you got any more great ideas and tips for UUID? Let me know and I’ll be sure to share them with others in the future posts.

Related books

If you want to learn more, here’s a great book:

See also:

• How to mount an ISO image
• Find large files and directories in Unix
• Using UUIDs – Ubuntu Help wiki
• How to find the default block size in Unix

Showing your processes in a hierarchical list is very useful for confirming the relationship between every process running on your system. Today I’d like to show you how you can get tree-like processes lists using various commands.

Showing processes tree with ptree

In Solaris, there’s quite a few commands which make the life of any system administrator much easier, they’re the process commands (p-commands). One of them which I particularly like is the ptree command which shows you a list of processes.

As you run the command, you get a hierarchical list of all the processes running on your Solaris system, along with process IDs (PIDs). To me, this is a very useful command, because it shows you how exactly each process relates to others in your system.

Here’s a fragment of the ptree output:

bash-3.00$ ptree
7     /lib/svc/bin/svc.startd
  250   /usr/lib/saf/sac -t 300
    268   /usr/lib/saf/ttymon
  260   -sh
    5026  -csh
9     /lib/svc/bin/svc.configd
107   /usr/lib/sysevent/syseventd
136   /usr/lib/picl/picld
140   /usr/lib/crypto/kcfd
159   /usr/sbin/nscd
227   /usr/sbin/rpcbind
234   /usr/lib/nfs/statd
235   /usr/sbin/keyserv
236   /usr/lib/netsvc/yp/ypserv -d
  237   rpc.nisd_resolv -F -C 8 -p 1073741824 -t udp
241   /usr/lib/nfs/lockd
247   /usr/lib/netsvc/yp/ypbind
263   /usr/lib/utmpd
286   /usr/sadm/lib/smc/bin/smcboot
  287   /usr/sadm/lib/smc/bin/smcboot
  288   /usr/sadm/lib/smc/bin/smcboot

Processes tree with pstree

In most Linux distributions, you can find a pstree command, very similar to ptree.

That’s how you may use it (-p is an option to show PIDs and -l uses long output format):

ubuntu$ pstree -pl
init(1)─┬─NetworkManager(5427)
        ├─NetworkManagerD(5441)
        ├─acpid(5210)
        ├─apache2(6966)─┬─apache2(2890)
        │               ├─apache2(2893)
        │               ├─apache2(7163)
        │               ├─apache2(7165)
        │               ├─apache2(7166)
        │               ├─apache2(7167)
        │               └─apache2(7168)
        ├─atd(6369)
        ├─avahi-daemon(5658)───avahi-daemon(5659)
        ├─bonobo-activati(7816)───{bonobo-activati}(7817)
...

Showing processes tree with ps –forest

ps command found in Linux has a –forest option, which shows you a tree structure of processes.

The best in my experience is to use it like this:

ubuntu$ ps -aef --forest
UID        PID  PPID  C STIME TTY          TIME CMD
...
107       5473     1  0 10037  4600   0 Apr28 ?        00:00:02 /usr/sbin/hald
root      5538  5473  0  5511  1288   0 Apr28 ?        00:00:00  \_ hald-runner
root      5551  5538  0  6038  1284   0 Apr28 ?        00:00:01      \_ hald-addon-input: Listening on /dev/input
107       5566  5538  0  4167   992   1 Apr28 ?        00:00:00      \_ hald-addon-acpi: listening on acpid socke
root      5600  5538  0  6038  1272   1 Apr28 ?        00:00:15      \_ hald-addon-storage: polling /dev/scd0 (ev
root      5476     1  0 10272  2532   0 Apr28 ?        00:00:00 /usr/sbin/console-kit-daemon
root      5627     1  0 12728  1176   1 Apr28 ?        00:00:00 /usr/sbin/sshd
root      9151  5627  0 17536  3032   0 10:53 ?        00:00:00  \_ sshd: greys [priv]
greys     9162  9151  0 17538  1892   1 10:54 ?        00:00:00      \_ sshd: greys@pts/3
greys     9168  9162  0  5231  3820   1 10:54 pts/3    00:00:00          \_ -bash
greys     9584  9168  0  3802  1124   0 11:27 pts/3    00:00:00              \_ ps -aeF --forest

This output is for demonstration purpose only, and so I’ve taken the first lines of the output out because they weren’t serving the purpose of this example very well.

For thins fragment of the output you can see how you get all the vital information about each process. I really like this way of running the ps command.

That’s it for today! Do you know any other neat way of looking at processes tree? Let me know!

Many software products, especially the commercial ones, are distributed as 32-bit packages. This means that they won’t be installed on your 64-bit system unless you clearly specify that you want to override the architecture dependency.

If you’re using Ubuntu or any other Debian based distribution, this post will teach you how to install 32-bit deb packages on your 64-bit OS.

Is it possible to run 32-bit applications on 64-bit OS?

In Unix world, yes: it is quite possible to run 32-bit binaries on 64-bit OS. There should generally be no problem, but there are, as always, a few caveats:

• your 64-bit system may need some 32-bit libraries installed just to make some old 32-bit software work (use getlibs in Ubuntu)
• even if 32-bit application runs on your 64-bit system, it will still have the 32-bit limitations
• some (especially commercial) software has hard-coded architecture checks which will prevent them from working in 64-bit mode. Although it’s a rather rare case, it still may happen and it probably means the developers had a really good reason for putting such limitations in

Why 32-bit packages don’t install on 64-bit by default

One of the main reasons is that if a certain software is provided in 32-bit configuration, it’s very likely to be available in 64-bit one as well. In Unix especially so, since a properly coded application can very easily be compiled for both architectures, especially if you have a 32-bit application and it’s only a matter of recompiling it in 64-bit.

It’s always best to have 64-bit version of the software, as it will run better and enjoy most optimal performance by running in the native mode and using 64-bit libraries of your OS.

The default behaviour is to let you know that you’re trying to install an architecturally incompatible piece of software, which should motivate you to double-check the availability of a 64-bit version. For example, this is what I get when installing a Skype for Linux on my Ubuntu 7.10 64-bit desktop:

ubuntu# dpkg -i ./skype-debian_2.0.0.63-1_i386.deb 
dpkg: error processing ./skype-debian_2.0.0.63-1_i386.deb (--install):
 package architecture (i386) does not match system (amd64)
Errors were encountered while processing:
 ./skype-debian_2.0.0.63-1_i386.deb

How To Install 32-bit Debian Packages on 64-bit System

Since I know there isn’t a 64-bit distribution of Skype, I would still like to install the package as it should work just fine. And the way to do this is to specify a –force-architecture option in dpkg command line:

ubuntu# dpkg -i --force-architecture ./skype-debian_2.0.0.63-1_i386.deb 
dpkg - warning, overriding problem because --force enabled:
 package architecture (i386) does not match system (amd64)
Selecting previously deselected package skype.
(Reading database ... 124455 files and directories currently installed.)
Unpacking skype (from .../skype-debian_2.0.0.63-1_i386.deb) ...
Setting up skype (2.0.0.63-1) ...

As you can see, we’re getting a warning, but the install went through just fine.

Warning: there’s a few further steps to get Skype working in 64-bit Ubuntu, so don’t take the above as a Skype how-to, these steps are out of the scope of this post though.

I see that my Finding Large Files and Directories post is quite popular, yet there are a few more ways to simplify your search for the largest disk space consumers in your Unix system.

Make find command show file sizes

If you remember, the default way a find command reports results includes only the fully qualified (that means including the full path) filenames.

Now, if you look at a task of identifying the largest files, it’s great if you can get a list of all the files bigger than some figure your specify, but what would be even better is to include the exact size of each file right into the output of the find command.

Here’s how you do it: it’s possible to specify which information about each file you’d like to see. Check out the find command man page for all the possibilities, but in today’s example I’m using two parameters: %s means the size of a file in bytes and %f means the filename itself.

Let’s say I want to get a list of all the files under /usr directory which are larger than 15Mb each, and show the exact size of each file. Here’s how it can be done:

ubuntu$ find /usr -size +15M -printf "%s - %p\n"
39859372 - /usr/lib/vmware/webAccess/java/jre1.5.0_07/lib/rt.jar
35487120 - /usr/lib/vmware/bin/vmware-hostd
16351166 - /usr/lib/vmware/bin/vmplayer
38353296 - /usr/lib/vmware/hostd/libtypes.so
54366585 - /usr/lib/vmware/hostd/docroot/client/VMware-viclient.exe
92143616 - /usr/lib/vmware/isoimages/linux.iso
23494656 - /usr/lib/vmware/isoimages/windows.iso
47070920 - /usr/lib/libgcj.so.81.0.0
20890468 - /usr/share/fonts/truetype/arphic/uming.ttf
17733780 - /usr/share/icons/crystalsvg/icon-theme.cache
18597793 - /usr/share/myspell/dicts/th_en_US_v2.dat
45345879 - /usr/src/linux-source-2.6.22.tar.bz2

Just to help you refresh your mind, here’s the explanation of all the parameters in the command line:

• /usr is the directory where we’d like to find the files of interest
• -size +15M narrows our interest to only the files larger than 15Mb
• -printf “%s – %p\n” is the magic which shows the nice list of files along with their sizes.

Sort the list of files by filesize

Next really useful thing we could do is to sort this list, just so that we could see a nice ordered representation of how big each file is. It’s very easily done by piping the output of the find command to a sort command:

ubuntu$ find /usr -size +15M -printf "%s - %p\n" | sort -n
16351166 - /usr/lib/vmware/bin/vmplayer
17733780 - /usr/share/icons/crystalsvg/icon-theme.cache
18597793 - /usr/share/myspell/dicts/th_en_US_v2.dat
20890468 - /usr/share/fonts/truetype/arphic/uming.ttf
23494656 - /usr/lib/vmware/isoimages/windows.iso
35487120 - /usr/lib/vmware/bin/vmware-hostd
38353296 - /usr/lib/vmware/hostd/libtypes.so
39859372 - /usr/lib/vmware/webAccess/java/jre1.5.0_07/lib/rt.jar
45345879 - /usr/src/linux-source-2.6.22.tar.bz2
47070920 - /usr/lib/libgcj.so.81.0.0
54366585 - /usr/lib/vmware/hostd/docroot/client/VMware-viclient.exe
92143616 - /usr/lib/vmware/isoimages/linux.iso

As you can see, the smallest files (just above 15Mb) are at the top of the list, and the largest ones are at the bottom.

Limit the number of files returned by find

The last trick I’ll show you today is going to make your task even easier: why look at the pages of find commnand output, if you’re after only the largest files? After all, your list can be much longer than the one shown above. To solve this little problem we’ll pipe the output of all the commands to yet another unix command, tail.

tail command allows you to show only a specified number of lines of any standard input or Unix text file you point it to. By default, it strips the number of lines to 10, which can be enough for your purposes.

Here’s how you can get a least of the 10 largest files under /usr:

ubuntu$ find /usr -size +15M -printf "%s - %p\n" | sort -n | tail
18597793 - /usr/share/myspell/dicts/th_en_US_v2.dat
20890468 - /usr/share/fonts/truetype/arphic/uming.ttf
23494656 - /usr/lib/vmware/isoimages/windows.iso
35487120 - /usr/lib/vmware/bin/vmware-hostd
38353296 - /usr/lib/vmware/hostd/libtypes.so
39859372 - /usr/lib/vmware/webAccess/java/jre1.5.0_07/lib/rt.jar
45345879 - /usr/src/linux-source-2.6.22.tar.bz2
47070920 - /usr/lib/libgcj.so.81.0.0
54366585 - /usr/lib/vmware/hostd/docroot/client/VMware-viclient.exe
92143616 - /usr/lib/vmware/isoimages/linux.iso

Show the largest 10 files in your Unix system

Now that you know all the most useful tricks, you can easily identify and show the list of the 10 largest files in your whole system. Bear in mind, that you should probably run this command with root privileges, as files in your system belong to various users, and a single standard user account will most likely have insufficient privileges to even list such files.

If you’re trying to locate your largest files in Ubuntu, use the sudo command (assuming you have the sudo privileges to become root):

ubuntu$ sudo find / -size +15M -printf "%s - %p\n" | sort -n | tail

alternatively, just become root by doing something like this (you obviously should know the root password to do that):

$ su - root 

and then run the find command itself. Here’s how the output looks on my Ubuntu desktop:

ubuntu$ find / -size +15M -printf "%s - %p\n" | sort -n | tail
39859372 - /usr/lib/vmware/webAccess/java/jre1.5.0_07/lib/rt.jar
45345879 - /usr/src/linux-source-2.6.22.tar.bz2
45356784 - /var/cache/apt/archives/linux-source-2.6.22_2.6.22-14.52_all.deb
45424028 - /var/cache/apt/archives/kde-icons-oxygen_4%3a4.0.2-0ubuntu1~gutsy1~ppa1_all.deb
47070920 - /usr/lib/libgcj.so.81.0.0
54366585 - /export/dist/vmware/server2b2/vmware-server-distrib/lib/hostd/docroot/client/VMware-viclient.exe
54366585 - /usr/lib/vmware/hostd/docroot/client/VMware-viclient.exe
92143616 - /export/dist/vmware/server2b2/vmware-server-distrib/lib/isoimages/linux.iso
92143616 - /usr/lib/vmware/isoimages/linux.iso
340199772 - /export/dist/vmware/server2b2/VMware-server-e.x.p-63231.x86_64.tar.gz

That’s it for today, hope this helps! Please bookmark this post if you liked it, and leave comments if there are any questions!

You probably know that modern Linux distributions have many things in common. Well, one of the reasons for this is LSB – Linux Standard Base. LSB is a joint project by a number of Linux vendors to standardize the OS environment.

From Linux Standard Base article on Wikipedia:

The goal of the LSB is to develop and promote a set of standards that will increase compatibility among Linux distributions and enable software applications to run on any compliant system. In addition, the LSB will help coordinate efforts to recruit software vendors to port and write products for Linux.

One of the immediate benefits of LSB compliancy is ability to confirm the exact information about your Linux release using the lsb_release command. By exact information I mean the release version, vendor name and most interestingly the codename of your current Linux release.

Red Hat Enterprise Linux LSB information

Here’s how a Red Hat Enterprise Linux 4 update 4 description will look:

bash-3.00$ lsb_release -a
LSB Version:    :core-3.0-amd64:core-3.0-ia32:core-3.0-noarch:graphics-3.0-amd64:graphics-3.0-ia32:graphics-3.0-noarch Distributor ID: RedHatEnterpriseWS
Description:    Red Hat Enterprise Linux WS release 4 (Nahant Update 4)
Release:        4
Codename:       NahantUpdate4

And here is RHEL5 LSB information:

bash-3.1$ lsb_release -a
LSB Version:    :core-3.1-amd64:core-3.1-ia32:core-3.1-noarch:graphics-3.1-amd64:graphics-3.1-ia32:graphics-3.1-noarch
Distributor ID: RedHatEnterpriseClient
Description:    Red Hat Enterprise Linux Client release 5 (Tikanga)
Release:        5
Codename:       Tikanga

SUSE Linux Enterprise Desktop (SLED10) LSB

For SUSE Linux Enterprise Desktop, LSB release information will look like this:

sled10~> lsb_release -a
LSB Version:    core-2.0-noarch:core-3.0-noarch:core-2.0-x86_64:core-3.0-x86_64:desktop-3.1-amd64:desktop-3.1-noarch:graphics-2.0-amd64:graphics-2.0-noarch:graphics-3.1-amd64:graphics-3.1-noarch
Distributor ID: SUSE LINUX
Description:    SUSE Linux Enterprise Desktop 10 (x86_64)
Release:        10
Codename:       n/a

Ubuntu LSB release information

In Ubuntu, I find the lsb_release information to be most informational – it’s concise but tells you everything you need:

ubuntu$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 7.04
Release:        7.04
Codename:       feisty

See also:

• How to Find Out the Release Version of Your Unix
• Bash: Find The Version of Your Shell

If you run your Ubuntu system behind a firewall and have to use proxy server for http and ftp access, then your apt-get on a newly installed Ubuntu system will probably not work.

To make it use proxy, simply set the http_proxy environment variable. Once you get it working (try something like apt-get update), you’ll probably want to add it to your .bashrc file.

Setting the http_proxy variable

Here’s how you set the variable:

bash$ export http_proxy=http://proxy:8080

If you’re required to use your username and password for your proxy, they can be specified this way. Obviously, port 8080 can and should be replaced with the valid port for your proxy server (sometimes it’s 3128):

bash$ export http_proxy=http://username:password@proxy:8080

See Also

• apt in Linux
• List installed packages on your Ubuntu Linux

If you have used your fresh Ubuntu install for longer than half an hour, chances are that you’ve discovered the sudo command already.

sudo allows certain users to execute a command under another user’s privileges. Most commonly, using sudo implies running a command as a superuser, but the approach works equally well for allowing you to inherit a user ID (uid) and group ID (gid) of any user on the system.

To gain access, a password is asked, and by default it is your password, and not the password of a user you’re trying to run a command as. This allows for the system’ s administrator to effectively manage user privileges without having any user share their password.

sudo is based off the /etc/sudoers file, which should be edited by root employing the visudo command. WARNING: although /etc/sudoers file is a regular text which root can edit manually, ONLY visudo way of updating it is recommended, as this command, apart from editing capabilities, also does a syntax check of the changes before applying them to prevent user privilege related disasters.

If you want to grant superuser privileges to a particular user, the following line should be added to the /etc/sudoers file (just type visudo to invoke the editor):

greys ALL=(ALL) ALL

In this example, greys is the username.

Related books

If you want to learn more, here’s a great book: