When I planned to move from Gurgaon to Pune I was in dilemma over whether to sell my Gurgaon registered car in Gurgaon or take it with me to Pune.
Since the new company I was joining was paying for relocation so car shifting cost was not an issue.
Solved: How to extend or grow a linux filesystem under LVM
In this post we will see how to grow a Linux filesystem without reboot.
- Let's check our current filesystem. We want to extend this filesystem by 200MB.
[root@cloudvedas CVFS1]# df -h /CVFS1 Filesystem Size Used Avail Use% Mounted on /dev/mapper/cvsvg-cldvdsvol1 47M 12M 32M 26% /CVFS1 [root@cloudvedas CVFS1]#
- First check if we have free space in VG
[root@cloudvedas /]# vgs VG #PV #LV #SN Attr VSize VFree cvsvg 1 1 0 wz--n- 196.00m 144.00m rhel 1 3 0 wz--n- 7.51g 36.00m [root@cloudvedas /]#
- Since we don't have 200MB free in "cvsvg" so we will add a new disk to it. First label the disk for LVM and get it under LVM control using pvcreate.
[root@cloudvedas CVFS1]# pvcreate /dev/sdb2 Physical volume "/dev/sdb2" successfully created [root@cloudvedas CVFS1]#
- Add the new partition to our VG.
[root@cloudvedas CVFS1]# vgextend cvsvg /dev/sdb2 Volume group "cvsvg" successfully extended [root@cloudvedas CVFS1]#
- Check the VG size again.
[root@cloudvedas CVFS1]# vgs VG #PV #LV #SN Attr VSize VFree cvsvg 2 1 0 wz--n- 444.00m 392.00m rhel 1 3 0 wz--n- 7.51g 36.00m [root@cloudvedas CVFS1]#
- Now we have the required space so, let's extend the volume first.
[root@cloudvedas CVFS1]# lvextend -L +200M /dev/cvsvg/cldvdsvol1 Size of logical volume cvsvg/cldvdsvol1 changed from 52.00 MiB (13 extents) to 252.00 MiB (63 extents). Logical volume cldvdsvol1 successfully resized
- On checking the LV we can see it's now extended as is now of 252MB.
[root@cloudvedas CVFS1]# lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert cldvdsvol1 cvsvg -wi-ao---- 252.00m root rhel -wi-ao---- 6.67g swap rhel -wi-ao---- 820.00m testvol1 rhel -wi-a----- 4.00m [root@cloudvedas CVFS1]#
- Let's increase the filesystem now using resize2fs.
[root@cloudvedas CVFS1]# resize2fs /dev/cvsvg/cldvdsvol1 resize2fs 1.42.9 (28-Dec-2013) Filesystem at /dev/cvsvg/cldvdsvol1 is mounted on /CVFS1; on-line resizing required old_desc_blocks = 1, new_desc_blocks = 2 The filesystem on /dev/cvsvg/cldvdsvol1 is now 258048 blocks long.
- Check the file system now.
[root@cloudvedas CVFS1]# df -h /CVFS1 Filesystem Size Used Avail Use% Mounted on /dev/mapper/cvsvg-cldvdsvol1 241M 13M 217M 6% /CVFS1 [root@cloudvedas CVFS1]#Great so we have now extended the filesystem.
Solved: How to label a disk in Linux
In this post we will see how to label a new disk in Linux and create a new LVM partition.
Step 1 Scan the new LUNS.
Step 2 List the available disks and identify the one you want to use.
Step 4 Now let's check our new partition
Step 1 Scan the new LUNS.
Step 2 List the available disks and identify the one you want to use.
fdisk -l |grep /dev/ |grep -v dmStep 3 Use fdisk to label the disk. Here we are using disk sdb .
[root@cloudvedas scsi_host]# fdisk /dev/sdb Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table Building a new DOS disklabel with disk identifier 0x909f2c7b. Command (m for help): p Disk /dev/sdb: 1073 MB, 1073741824 bytes, 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x909f2c7b Device Boot Start End Blocks Id System Command (m for help):Step 4 Create Primary partition using option "n" of size 200MB.
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1):
First sector (2048-2097151, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-2097151, default 2097151): +200M
Partition 1 of type Linux and of size 200 MiB is set
(Don't miss the + used before 200M. It's very critical else it won't work as expected)Step 4 Now let's check our new partition
Command (m for help): p Disk /dev/sdb: 1073 MB, 1073741824 bytes, 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xc1c8c781 Device Boot Start End Blocks Id System /dev/sdb1 2048 411647 204800 83 Linux Command (m for help):Step 5 In the above output we can see that the new partition is a standard linux partition. Let's Change the partition type to Linux LVM. Here we will use "8e" which is a Hex code for LVM. You can type L to list all codes.
Command (m for help): t Selected partition 1 Hex code (type L to list all codes): 8e -Changed type of partition 'Linux' to 'Linux LVM' Command (m for help): p Disk /dev/sdb: 1073 MB, 1073741824 bytes, 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xc1c8c781 Device Boot Start End Blocks Id System /dev/sdb1 2048 411647 204800 8e Linux LVM Command (m for help):Step 6 Finally save the changes with option "w"
Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.Step 7 Let's list the partition table to cross check that our partition table is saved correctly.
[root@cloudvedas /]# fdisk -l /dev/sdb Disk /dev/sdb: 1073 MB, 1073741824 bytes, 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x0aa5ab95 Device Boot Start End Blocks Id System /dev/sdb1 2048 411647 204800 8e Linux LVM [root@cloudvedas /]#Cool! So, we have now a LVM partition which we can bring under LVM control using pvcreate.
LVM Crash course
In this post we will give you a crash course on Linux LVM (Logical Volume Manager). This post will cover the most used LVM commands in a Linux Admin life.
Before we start first let's go through the concepts.
Physical Volumes (PVs): Storage devices (physical hard disks, partitions, RAID arrays etc.) provides raw storage
Volume Groups (VGs): Combine multiple PVs to create a group. They can be mirror or concatenation of PVs.
Logical Volumes (LVs): Create smaller volumes from the Volume Group(VG) as per your size requirement. You can can use the LVs to create filesystem on them.
Below commands are for RHEL 7.
All the below commands will require root access. You can either run them with sudo or switch to root user as mentioned below.
Create PV (Physical Volume)
-i|--stripes (Number of disks in stripe)
-I|Stripe size
Extend LV
Ensure filesystem is unmounted before running this
Before we start first let's go through the concepts.
Physical Volumes (PVs): Storage devices (physical hard disks, partitions, RAID arrays etc.) provides raw storage
Volume Groups (VGs): Combine multiple PVs to create a group. They can be mirror or concatenation of PVs.
Logical Volumes (LVs): Create smaller volumes from the Volume Group(VG) as per your size requirement. You can can use the LVs to create filesystem on them.
Below commands are for RHEL 7.
All the below commands will require root access. You can either run them with sudo or switch to root user as mentioned below.
sudo su -Install LVM
[root@cloudvedas ~]# yum install lvm2*Check LVM version
[root@cloudvedas ~]# lvm versionLabel the new disk and bring it under LVM using pvcreate
Create PV (Physical Volume)
[root@cloudvedas ~]# pvcreate /dev/sdb1Show PV
[root@cloudvedas ~]# pvs /dev/sdb1Create VG (Volume Group)
[root@cloudvedas ~]# vgcreate cvsvg /dev/sdb1Show VG
[root@cloudvedas ~]# vgs cvsvgDisplay VG
[root@cloudvedas ~]# vgdisplay cvsvgExtend VG
[root@cloudvedas ~]# vgextend cvsvg /dev/sdb2Create LV (Logical Volume)
[root@cloudvedas ~]# lvcreate -L 500M cvsvg -n cldvdsvol1Display LV
[root@cloudvedas ~]# lvdisplay /dev/cvsvg/cldvdsvol1Create mirror volume
lvcreate -L 100M -m1 -n cvmirrorvol1 cvsvgCreate striped volume
[root@cloudvedas ~]# lvcreate -L 50M -i 3 -I 64 -n stripevol cvsvgHere
-i|--stripes (Number of disks in stripe)
-I|Stripe size
Extend LV
lvextend -L +20M /dev/cvsvg/stripevolDe-activate volume
lvchange -an /dev/cvsvg/stripevolActivate volume
lvchange -ay /dev/cvsvg/stripevolRemove LV
Ensure filesystem is unmounted before running this
lvremove /dev/cvsvg/stripevolCreate filesystem
mkfs -t ext4 /dev/cvsvg/cldvdsvol1Create directory
mkdir /CVFS1Mount filesystem
mount /dev/cvsvg/cldvdsvol1 /CVFS1All the available LVM commands
[root@cloudvedas ~]# lvm help Available lvm commands: Use 'lvm help <command>' for more information devtypes Display recognised built-in block device types dumpconfig Dump configuration formats List available metadata formats help Display help for commands lvchange Change the attributes of logical volume(s) lvconvert Change logical volume layout lvcreate Create a logical volume lvdisplay Display information about a logical volume lvextend Add space to a logical volume lvmchange With the device mapper, this is obsolete and does nothing. lvmdiskscan List devices that may be used as physical volumes lvmsadc Collect activity data lvmsar Create activity report lvreduce Reduce the size of a logical volume lvremove Remove logical volume(s) from the system lvrename Rename a logical volume lvresize Resize a logical volume lvs Display information about logical volumes lvscan List all logical volumes in all volume groups pvchange Change attributes of physical volume(s) pvresize Resize physical volume(s) pvck Check the consistency of physical volume(s) pvcreate Initialize physical volume(s) for use by LVM pvdata Display the on-disk metadata for physical volume(s) pvdisplay Display various attributes of physical volume(s) pvmove Move extents from one physical volume to another pvremove Remove LVM label(s) from physical volume(s) pvs Display information about physical volumes pvscan List all physical volumes segtypes List available segment types tags List tags defined on this host vgcfgbackup Backup volume group configuration(s) vgcfgrestore Restore volume group configuration vgchange Change volume group attributes vgck Check the consistency of volume group(s) vgconvert Change volume group metadata format vgcreate Create a volume group vgdisplay Display volume group information vgexport Unregister volume group(s) from the system vgextend Add physical volumes to a volume group vgimport Register exported volume group with system vgmerge Merge volume groups vgmknodes Create the special files for volume group devices in /dev vgreduce Remove physical volume(s) from a volume group vgremove Remove volume group(s) vgrename Rename a volume group vgs Display information about volume groups vgscan Search for all volume groups vgsplit Move physical volumes into a new or existing volume group version Display software and driver version information [root@cloudvedas ~]#
Solved: How to schedule a cron job in Linux or Solaris
In this post we will see what’s a cron job and how we can set it.
Cron is managed by a crontab file. Its a configuration file in which we can schedule shell command to run periodically.
Scheduling cron
For modifying a cron you use a utility called crontab .
Before you can execute any crontab command you will have to set environment variables by executing below commands in your linux or unix command prompt.
Display current cron jobs
You have to follow a specific format to schedule a cron job. See e.g. below:
* * * * * /file_execute.sh
– – – – –
| | | | |
| | | | +—– day of week (0 – 6) (Sunday=0)
| | | +——- month (1 – 12)
| | +——— day of month (1 – 31)
| +———– hour (0 – 23)
+————– min (0 – 59)
From the table above we can interpret that the cron job will execute backup.sh file at 22:30 every saturday
Let’s take a few more examples
Execute every 5 mins
What if you want the cron to run at 22:30:30 i.e exact to seconds.
In such case at the start of your shell script put a sleep command as below
Log redirection
Saving a cron file
Once you are done with cron schedule modification don’t forget to save the file.
You can save the file using standard save method of vi editor. The command sequence to save is Esc :wq!
Cron is managed by a crontab file. Its a configuration file in which we can schedule shell command to run periodically.
Scheduling cron
For modifying a cron you use a utility called crontab .
Before you can execute any crontab command you will have to set environment variables by executing below commands in your linux or unix command prompt.
TERM=vt100
EDITOR=vi
export TERM
export EDITORNow let’s see the different crontab commands.
Display current cron jobs
crontab -lEdit cron file
crontab -eRemove cron file (Be extremely careful with this command)
crontab -rCron format
You have to follow a specific format to schedule a cron job. See e.g. below:
30 22 * * 6 /home/cldvds/scripts/backup.shLet’s learn more about the asterisk (*) .
* * * * * /file_execute.sh
– – – – –
| | | | |
| | | | +—– day of week (0 – 6) (Sunday=0)
| | | +——- month (1 – 12)
| | +——— day of month (1 – 31)
| +———– hour (0 – 23)
+————– min (0 – 59)
From the table above we can interpret that the cron job will execute backup.sh file at 22:30 every saturday
Let’s take a few more examples
Execute every 5 mins
*/5 * * * * /home/cldvds/scripts/backup.shExecute every hour
0 * * * * /home/cldvds/scripts/backup.shExecute in every 3 hours
0 */3 * * * /home/cldvds/scripts/backup.shExecute every Sunday at 1 am
0 1 * * 0 /home/cldvds/scripts/backup.shTip:-
What if you want the cron to run at 22:30:30 i.e exact to seconds.
In such case at the start of your shell script put a sleep command as below
sleep 30So, now the script will wait for 30 secs before executing.
Log redirection
30 22 * * 6 /home/cldvds/scripts/backup.sh >> /home/cldvds/scripts/logs.txt 2>&1With the above command stderr (standard error) and stdout (standard output) will go to your logs.txt file.
Saving a cron file
Once you are done with cron schedule modification don’t forget to save the file.
You can save the file using standard save method of vi editor. The command sequence to save is Esc :wq!
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