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Gleb Reys

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atime, ctime and mtime in Unix filesystems

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atime-ctime-mtime
atime, ctime and mtime in Linux

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).

File and directory timestamps in Unix

Three times tracked for each file in Unix are these:

  • access time – atime
  • change time –  ctime
  • modify time –  mtime

INTERESTING: there's no file creation timestamp kept in most filesystems – meaning you can't run a command like "show me all files created on certain date". This said, it's usually possible to deduce the same from ctime and mtime (if they match – this probably means that's when the file was created).

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How To List Directories in a Directory in Unix

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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.

Using find to show only directories

find command helps you show only the directories by using a -type d parameter.

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How To Find a Location of a Directory in Unix

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Very quick tip for you today, I just see that many of visitors of this block are curious how they can find a directory in Unix – and so here's a command to help you do just that.

Finding directories in Unix

There's nothing better than to employ the find command. As you might remember, among many things, this wonderful tool allows you to search files by their type. Since nearly everything in Unix is a file, this means you can find directories.

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How To Find the Default Block Size in Unix

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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.

Default block size in Linux

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.

Default block size in Solaris

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).

Using df -g to confirm the filesystem block size

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       0x00000004 flag             255 filename length

Using fstyp -v to confirm the filesystem block size

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

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

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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:

How To Find the Largest Files in your Unix system

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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.

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Find Out Linux Version using Linux Standard Base (LSB) files

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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.

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