mtime, ctime, and atime timestamp Linux

Recently, I've implemented a caching system. This involve removing old file from the cache. One important factor for making a decision is a file timestamp. There are many timestamp implemented in the file system here are method for viewing timestamp info.

mtime, ctime, and atime

atime - access time
mtime - if modify time
ctime - of change time

To view atime

ls -lu

To view ctime

ls -lc

To view mtime

ls -lt

Access time is when last time data from the file was access.

Modify time is when last change was done to the file.

Change time id when you change owner.

Or

Use stat command

stat filename

stat newname2.txt

File: `newname2.txt'

Size: 13 Blocks: 8 IO Block: 4096 regular file

Device: 805h/2053d Inode: 2338058 Links: 1

Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)

Access: 2011-01-28 16:01:10.000000000 +0700

Modify: 2011-01-28 16:02:35.000000000 +0700

Change: 2011-01-28 16:06:26.000000000 +0700

to verify with ls command

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References :

http://baliyansandeep.blogspot.com

Gentoo migration to raid

At some point, high availability become more essential to your server. Raid1(mirror) can help server to be able to continue even the disk go wrong. This blog is intend to be a complete just-type-guide for system admin. I hope that you guy succeeded in this migration

Background my system is gentoo on sda. The new disk will be sdb. After finishing copying data to sdb. The another new disk will be replace as sda. sda and sdb will be raid1 mirroring each other.

#0 move running service to another system

- make sure that the system can be down for maintainance

#1 shutdown system

shutdown -h now

#2 install new hdd as sdb

some vendor disable port B (for sdb) please make sure that it is enable so it can be visible from linux.

#3 boot system with live cd

modprobe raid1

#4 format disk and create raid on sdb

available 500GB

-> sdb1 boot 1GB ext2

-> sdb5 root entire ext3

-> sdb6 swap 4GB swap

cfdisk /dev/sdb

cd /dev && MAKEDEV md

mdadm --create /dev/md1 --level=1 --raid-devices=2 missing /dev/sdb1

mdadm --create /dev/md5 --level=1 --raid-devices=2 missing /dev/sdb5

mke2fs /dev/md1

mke2fs -j /dev/md5

mkswap /dev/sdb6

swapon /dev/sdb6

#5 copy data from sda to raid

mkdir /mnt/gentoo1

mount /dev/sda5 /mnt/gentoo1

mount /dev/md5 /mnt/gentoo

mount /dev/sda1 /mnt/gentoo1/boot

mkdir /mnt/gentoo/boot

mount /dev/md1 /mnt/gentoo/boot

cp -dpRx /mnt/gentoo1/* /mnt/gentoo/

#6 install boot loader to raid

mount -t proc none /mnt/gentoo/proc

mount -o bind /dev /mnt/gentoo/dev

chroot /mnt/gentoo /bin/bash

env-update

source /etc/profile

export PS1=”(chroot) $PS1”

#Edit grub.conf change root=/dev/sdaxx to mdxx

nano /boot/grub/grub.conf

#install boot loader to the disk

grub –no-floppy

- device (hd0) /dev/sdb

- root (hd0,0)

- setup (hd0)

#7 edit fstab to mount disk on raid instead // or just copy from preedit @ /home/username/fstab

nano /etc/fstab

#8 shutdown & replace sda with new disk

exit

cd /

umount /mnt/gentoo/boot /mnt/gentoo/proc /mnt/gentoo/dev /mnt/gentoo

umount /mnt/gentoo1/boot /mnt/gentoo1

shutdown -h now

-replace new disk

#9 sync disk and install boot loader

-change bios priority to start boot from sdb

sfdisk -d /dev/sdb | sfdisk /dev/sda

mdadm --add /dev/md1 /dev/sda1

mdadm --add /dev/md5 /dev/sda5

#edit fstab add sda as swap

nano /etc/fstab

mkswap /dev/sda6

swapon /dev/sda6

grub –no-floppy

- device (hd0) /dev/sda

- root (hd0,0)

- setup (hd0)

#wait until sync finish

- reboot test

- restore bios boot priority

- restore sevice back to the server.