Sunday, August 17, 2014
Tuesday, August 12, 2014
Step By Step Linux Boot Process [Updated]
In systemd based systems (RHEL7/8, SLES15 etc..)
Power On → BIOS/UEFI → MBR/GPT → GRUB2 (Stage 1 Boot Loader → Stage 2 Boot Loader) → Kernel → systemd → Login
Power On → BIOS/UEFI → MBR/GPT → GRUB2 (Stage 1 Boot Loader → Stage 2 Boot Loader) → Kernel → systemd → Login
→ Power On
The system/server hardware or firmware either UEFI (Unified Extensible Firmware Interface) Or BIOS (Basic Input Output System) runs Power On Self Test (POST) when system gets powered-on.
The system/server hardware or firmware either UEFI (Unified Extensible Firmware Interface) Or BIOS (Basic Input Output System) runs Power On Self Test (POST) when system gets powered-on.
Wednesday, August 6, 2014
Restore A Missing Physical Volume
Let's find out the step-by-step involved to recover a failed physical volume in Linux.
The setup has got the"testvg" which got "testlv" and corresponding Physical Volume (PV) is on '/dev/sdb' block device as shown below:
The setup has got the"testvg" which got "testlv" and corresponding Physical Volume (PV) is on '/dev/sdb' block device as shown below:
[root@RHEL4 archive]# vgs
VG #PV #LV #SN Attr VSize VFree
VolGroup00 1 2 0 wz--n- 19.88G 32.00M
testvg 1 1 0 wz--n- 200.00M 0 ← targeted VG
[root@RHEL4 archive]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 VolGroup00 lvm2 a- 19.88G 32.00M
/dev/sdb testvg lvm2 a- 200.00M 0 ← targeted PV
[root@RHEL4 archive]# lvs
LV VG Attr LSize Origin Snap% Move Log Copy%
LogVol00 VolGroup00 -wi-ao 18.88G
LogVol01 VolGroup00 -wi-ao 992.00M
testlv testvg -wi-a- 200.00M ← targeted LV
Backup And Restore A Hard Drive/Disk Partition Table
This is a small demonstration on how to backup and restore partition table data in a Linux system. For this demo, I've taken '/dev/sde' hard drive as an example. So, in the first part, I'd backup the drive partition table and later part we'd destroy the data, hence, we'd restore it finally using the backup copy.
1) The device '/dev/sde' which got one partition '/dev/sde1' with a label '/label_test' mounted on '/test2' as seen below:
{Checking the partition details of the device}
[root@RHEL4 ~]# fdisk -l /dev/sde
Disk /dev/sde: 213 MB, 213909504 bytes
64 heads, 32 sectors/track, 204 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Device Boot Start End Blocks Id System
/dev/sde1 1 204 208880 83 Linux
Allow Regular User To Run Administrative Commands
- To achieve this, one would need to add the users and respective commands to '/etc/sudoers' file.
- Run the command : visudo
- This command would open up '/etc/sudoers' file in edit mode and doesn't allow another user to open the file and edit in any other terminal.
- Say for example, we'd need to allow user 'bkp' to run the 'mke2fs' command then we could add the below line in '/etc/sudoers' to accomplish this task:
bkp ALL=/sbin/mke2fs
- After this change, the user 'bkp' would need to run the command with 'sudo' as given below:
$ sudo /sbin/mke2fs -n /dev/sdb1
<< this would prompt for password, so after successful authentication, it would run the administrative command by the user bkp >>
- Other users except 'root' cannot execute commands under /sbin
- Run the command : visudo
- This command would open up '/etc/sudoers' file in edit mode and doesn't allow another user to open the file and edit in any other terminal.
- Say for example, we'd need to allow user 'bkp' to run the 'mke2fs' command then we could add the below line in '/etc/sudoers' to accomplish this task:
bkp ALL=/sbin/mke2fs
- After this change, the user 'bkp' would need to run the command with 'sudo' as given below:
$ sudo /sbin/mke2fs -n /dev/sdb1
<< this would prompt for password, so after successful authentication, it would run the administrative command by the user bkp >>
- Other users except 'root' cannot execute commands under /sbin
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