Learn UNIX
April 24th, 2008 — News
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For all of you who were waiting for the next release of Ubuntu, it's finally here! I've been using the beta of Ubuntu 8.04 (Hardy Heron) for the past month or so, and found it an excellent release to work with.
April 11th, 2008 — News
As you know, Unix filesystems store a number of timestamps for each file. This means that you can use these timestamps to find out when any file or directory was last accessed (read from or written to), changed (file access permissions were changed) or modified (written to).
Three times tracked for each file in Unix are these:
April 9th, 2008 — News
Another quick answer to the question I see a lot in search queries on this blog: listing directories in a directory. I take it that this question means showing a list of only the directories and not other files under a certain location of your Unix filesystem.
find command helps you show only the directories by using a -type d parameter.
April 2nd, 2008 — News
The questions about default block sizes used in your Unix system are always popular. Today I'd like to show you a few ways to answer them.
If you ever want to confirm the block size of any filesystem of Ubuntu or any other Linux OS, tune2fs command is here to help:
ubuntu# tune2fs -l /dev/sda1 | grep Block Block count: 4980736 Block size: 4096 Blocks per group: 32768
From this example, you can see that the default block size for the filesystem on /dev/sda1 partition is 4096 bytes, or 4k. That's the default block size for ext3 filesystem.
The default block size in Solaris is 8192 bytes, or 8k. However, some architectures allow you to use 4k size as well, by specifying it as a command line option for the newfs command.
To be absolutely sure, you can use one of the commands: df -g (takes a filesystem mount point name as the parameter - / or /usr for example) or use fstyp -v command (needs a character device of the filesystem you're interested in).
This command can be used as any user, so to confirm a block size for any of the filesystems you don't have to be root. However, it works only for mounted filesystems.
bash-3.00$ df -g / / (/dev/dsk/c1t0d0s0 ): 8192 block size 1024 frag size 12405898 total blocks 4399080 free blocks 4275022 available 751296 total files 603544 free files 30932992 filesys id ufs fstype 0×00000004 flag 255 filename length
Because this command accesses the character device of a particular filesystem, you have to be root to run it. But as a bonus compared to df -g, you can use fstyp -v on an unmounted filesystem:
bash-3.00# fstyp -v /dev/dsk/c1t0d0s0 | grep ^bsize bsize 8192 shift 13 mask 0xffffe000
March 11th, 2008 — News
When you're trying to clean up your filesystems and reclaim some space, one of the first things you'll want to do is to confirm the largest directories and individual files you have. This can be easily done using two Unix commands: find command and du command.
It's very simply to find files which are larger than a specified size. The find command accepts a size parameter, and you can specify the limits for file sizes in your command line.
February 7th, 2008 — News
If you need to compare two text files in Unix, you're mostly likely to use the diff command.
Today I'll talk about the simplest scenario: you want to compare two files and understand if there are any differences.
January 23rd, 2008 — News
There's quite a few ways to confirm a user ID (uid) in Unix.
This is probably one of the easiest ways to find out a uid of a particular user in your system:
# id -u greys 500
The most common way of using the id command is even simpler, and it gives you all the information about a user you may need:
# id greys uid=500(greys) gid=500(greys) groups=500(greys)
This not only shows you the user id (uid), but also confirms user's group id (gid) and all the rest Unix groups a user belongs to.
January 9th, 2008 — Advanced topics, News, Solaris
This is a very brief introduction into navigating the device paths in Solaris. I'm using a Solaris 10 installed on Sun v490 for all the commands shown below.
Even though all the block and character special device files are traditionally found under /dev directory, if you look closer at your Solaris 10 setup you will notice that they're not the device files themselves, but instead are just symbolic links to device files under /devices directory.
Solaris uses /devices directory for representing all the physical hierarchy of installed devices and buses found on your hardware system.
January 3rd, 2008 — News
Looking at this website access logs, I see how many people share the same problems and look for the same solutions, but use vastly different search queries to get to my posts.
I've decided to make your life easier, and have just launched a Unix Tutorial Reference page, which is an index of pages based on your searches. Most pages will have a basic introduction to the topic and provide further pointers to the solution posts.
September 20th, 2007 — Basic stuff, Linux, News, Ubuntu
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.