Linux Disable /var Access Time Updates ( noatime )

Posted on in Categories , , , , , last updated November 27, 2009

I‘ve configured and mounted /var for squid caching and other purposes under Linux. I’ve noticed that the Linux file system keeps records of when files are created, updated, and accessed. My /var is exclusively used for caching purpose and I do not want to waste disk I/O while updating last-time-read attribute during reads and writes to files. How do I disable access time updates for /var partition?

Linux / UNIX: Cannot Preserve Ownership Error when Files are Moved or Copied

Posted on in Categories , , , , , , , , , last updated September 21, 2007

Q. I’m using CentOS Linux. I’m getting an error – Cannot Preserve Ownership, when I try to copy files from Linux ext3 to FAT32 or files moved to an NFS NAS server mount point. How do I fix this error and copy / move files?

A. Generally you use command like cp or my to copy file. While copying a file these command try to copy file attributes such as ACL information or group access information etc. FAT32 and NFS mount mount cannot support all sort of attributes and these commands cannot differentiate between a filesystem that doesn’t support ACL and Linux file system permission.

All your files will be copied or moved without ACL and permissions. You can ignore this error and files should be copied / moved successfully.

Linux / UNIX: Display file inode (index number)

Posted on in Categories , , , , , , , , , last updated August 20, 2007

Q. How do I display file inode number using command line?

A. An inode is a data structure on a Unix / Linux file system. An inode stores basic information about a regular file, directory, or other file system object. You can use following two commands to display an inode:
[a] ls command : list directory contents

[b] stat command : display file or file system status

ls command

Type ls command with -i ( print the index number of each file ) option:
$ ls -i /etc/passwd
Output:

752010 /etc/passwd

752010 is index number (inode) for /etc/passwd file.

stat command

$ stat /etc/passwd
Output:

  File: `/etc/passwd'
  Size: 2026            Blocks: 8          IO Block: 4096   regular file
Device: 811h/2065d      Inode: 752010      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2007-08-20 23:19:20.000000000 +0530
Modify: 2007-07-07 00:06:56.000000000 +0530
Change: 2007-07-07 00:06:56.000000000 +0530

You can use inode number to delete or search a file.

Can I run fsck or e2fsck when Linux file system is mounted?

Posted on in Categories , , last updated October 29, 2007

Q. Can I run fsck or e2fsck command when Linux file system is mounted? Do you advice to run fsck on a live file system? I am using Cent OS.

A. No. Do not run fsck on a live or mounted file system. fsck is used to check and optionally repair one or more Linux file systems. Running fsck on a mounted filesystem can usually result in disk / data corruption. So please do not do it. You have two choices
(a) Take down system to single user mode and unmout system

(b) Boot from the installation CD into rescue mode

(a) Take down system to single user mode and unmout system

Following are steps :
=> Use init (process control initialization ) command to change runlevel 1 (singe user mode)
=> Use umount command to unmount /home file system
=> Run fsck using fsck command

Let us say you would like to run fsck on /home (/dev/sda3):

# init 1
# umount /home
# umount /dev/sda

# fsck /homeOR
# fsck /dev/sda3OR
# e2fsck -y /dev/sda3

(b) Boot from the installation CD into rescue mode

If you are using Cent OS/Fedora Core/RHEL linux, boot from first CD and at boot prompt type linux rescue nomount:
boot: linux rescue nomount

Now make new node for disk and partition 3:
# mknod /dev/sda
# mknod /dev/sda3
# fsck /dev/sda3

OR
# e2fsck -y /dev/sda3

Don’t forget to reboot the system:
# exit;exit
# reboot