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Shrink Linux Swap File Size CentOS

Hi,

I've had my server running for 6 years without any real need for a large swap file. The partition with the swap file is running out of space. I'd like to free up space by reducing the size of the swap file. Could someone give me the steps and specific commands to shrink or make a new smaller swap file? I'd like to have a 1GB swap file - Not a 32GB swap file. -- you can see from my top command that in the last 93 days I've only used 80K of the swap.

I'm running CentOS

Here is information that I've gathered which may be helpful. Let me know if you need any other information.

Thank you in advance for your help.

The swap file is in the /home directory

root@cv2 [~]# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/sda6                               partition       2097144 80      0
/home/swap/systemswap                   file            31999992        0       -1

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root@cv2 [/home/swap]# ls -lh
total 31G
-rw-r--r-- 1 root root 31G Oct 30  2011 systemswap

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root@cv2 [/etc]# grep Swap /proc/meminfo
SwapCached:           80 kB
SwapTotal:      34097136 kB
SwapFree:       34097056 kB

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root@cv2 [/etc]# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2       9.9G  4.0G  5.4G  43% /
tmpfs            56G  5.8G   50G  11% /dev/shm
/dev/sda1        99M   71M   23M  76% /boot
/dev/sda8       198G  186G  2.0G  99% /home
/dev/sda7      1008M  117M  840M  13% /tmp
/dev/sda3       9.9G  9.4G   15M 100% /usr
/dev/sda5       9.9G  4.7G  4.8G  50% /var
/dev/sdb1       1.1T  970G   74G  93% /disk1

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top - 22:40:38 up 93 days,  6:27,  2 users,  load average: 8.03, 5.80, 5.03
Tasks: 1929 total,   5 running, 1924 sleeping,   0 stopped,   0 zombie
Cpu(s):  8.1%us,  2.9%sy,  0.0%ni, 85.5%id,  2.8%wa,  0.0%hi,  0.8%si,  0.0%st
Mem:  115595148k total, 88334512k used, 27260636k free,   316568k buffers
Swap: 34097136k total,       80k used, 34097056k free,  7282052k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 6604 mysql     20   0 95.0g  69g  11m S 200.4 62.6 191014:01 mysqld
 8685 nobody    20   0 1882m 614m 2396 S 62.3  0.5 174:29.26 memcached
46512 nobody    20   0  220m  81m 6088 S  0.0  0.1   0:58.35 httpd
55380 nobody    20   0  198m  59m 5996 S  0.0  0.1   0:08.45 httpd
35678 nobody    20   0  176m  36m 5616 S  0.3  0.0   0:12.33 httpd
 1181 nobody    20   0  172m  32m 6120 S  2.0  0.0   0:18.90 httpd
11305 nobody    20   0  170m  30m 6008 S  1.6  0.0   0:32.45 httpd

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In preparation , I made a copy of my /etc/fstab file. This is what it looks like

# /etc/fstab
# Created by anaconda on Thu Oct 27 00:34:52 2011
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=974d8ad5-7b3b-4e76-a15e-883a26e069b0 /                       ext4    defaults,noatime        1 1
UUID=b5e08c39-eb88-44c1-aa67-6f4873ef616e /boot                   ext2    defaults,noatime        1 2
UUID=30b03ace-e109-4c17-b7f5-d65d9844d9db /home                   ext4    defaults,noatime        1 2
UUID=126a480d-e7e7-4620-b28e-b95c0bc17dab /tmp                    ext4    defaults,noatime        1 2
UUID=4858ba50-62db-45ae-860b-9df020a1abfd /usr                    ext4    defaults,noatime        1 2
UUID=92df8c83-6892-4d14-ad7b-04f173053cd9 /var                    ext4    defaults,noatime        1 2
UUID=4923b91a-942c-4283-8597-85d63514e29e swap                    swap    pri=0,defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/tmp             /var/tmp                    ext3    defaults,bind,noauto        0 0
/dev/sdb1                /disk1                ext4    defaults,noatime        1 2
/home/swap/systemswap   swap                    swap    defaults,noatime        0 0
# //10.10.10.99/SL999999-1 /mnt/nas cifs rw,username=SL999999-1,password=XXXXXXXX 0 0
#/dev/sdb1               /disk1                ext4    defaults,atime,strictatime,norelatime        1 2
#
# mysql_cache is in RAM used for file based sql caching
#tmpfs           /disk1/mysql_cache     tmpfs   size=1500m 0 0

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root@cv2 [/dev]# free -m
             total       used       free     shared    buffers     cached
Mem:        112885      88629      24255       4268       2626       9617
-/+ buffers/cache:      76386      36499
Swap:        33297          0      33297

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root@cv2 [/home/swap]# fdisk -l

Disk /dev/sdb: 1198.3 GB, 1198295875584 bytes
255 heads, 63 sectors/track, 145684 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000a25cb

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1      145684  1170206698+  83  Linux

Disk /dev/sda: 250.8 GB, 250808893440 bytes
255 heads, 63 sectors/track, 30492 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0009164a

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          14      104448   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              14        1319    10485760   83  Linux
/dev/sda3            1319        2624    10485760   83  Linux
/dev/sda4            2624       30493   223853568    5  Extended
/dev/sda5            2625        3930    10485760   83  Linux
/dev/sda6            3930        4191     2097152   82  Linux swap / Solaris
/dev/sda7            4191        4322     1048576   83  Linux
/dev/sda8            4322       30493   210217984   83  Linux
root@cv2 [/home/swap]#

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Natty Greg

How much ram do you have the machine -- cause the swap space allocated even though not being used up fully is normally twice the size of the amount of ram installed, if cpu n ram is under heavy load it will normally use the space to park files stored in ram for offloading once cpu is less busy, u cannot use the average to truly know you'd have to monitor the machine over a period to see how it utilized it.

More is better, less could be trouble

U_S_A

ASKER

@Natty,

I think my top command screen shot, in my question answers the question of how much RAM I have - I could be wrong though.
Mem: 115595148k total

How do I know if my Swap had been used in the last 90 days? I think top command also gives me that information, unless I don't understand that too.
Swap: 34097136k total, 80k used, 34097056k free, 7282052k cached
Is it 80K?

top also shows typical load on my machine 24x7 ,,, in fact it typically is less load.

Natty Greg

Make sense in my little hast to skim the info

Natty Greg

Here you go sir

Let’s begin but first turning off swap on the Swap Logical Volume

# swapoff /dev/VolGroup00/LogVol01

Once swap is off let’s take the disk space we require.

# lvresize -L -4GB /dev/VolGroup00/LogVol01
WARNING: Reducing active logical volume to 896.00 MB
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce LogVol01? [y/n]: y
Reducing logical volume LogVol01 to 896.00 MB
Logical volume LogVol01 successfully resized

Now let’s add what we removed to the main Logical Volume.

# lvresize -L +4GB /dev/VolGroup00/LogVol00
Extending logical volume LogVol00 to 9.00 GB
Logical volume LogVol00 successfully resized

Resize the File System

# resize2fs -p /dev/VolGroup00/LogVol00
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/VolGroup00/LogVol00 is mounted on /; on-line resizing required
Performing an on-line resize of /dev/VolGroup00/LogVol00 to 2359296 (4k) blocks.
The filesystem on /dev/VolGroup00/LogVol00 is now 2359296 blocks long.

Rebuild the swap partition.

# mkswap /dev/VolGroup00/LogVol01
Setting up swapspace version 1, size = 939520 kB

Turn swap on.

# swapon /dev/VolGroup00/LogVol01

Let’s check the amount of disk space available and LVM attributes to see if our changes took effect.

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
8.8G 2.4G 6.0G 28% /
/dev/xvda1 99M 23M 72M 25% /boot
tmpfs 4.0G 0 4.0G 0% /dev/shm

You can get the full scoup here if you want to double check how to do the swap space shrink

http://www.how2centos.com/centos-lvm-resizing-guide/

ASKER CERTIFIED SOLUTION

arnold

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U_S_A

ASKER

@Natty, I was hoping for exact commands that I would use in my setup. Not a copy/paste from someone's guide. I found many guides, but was to afraid to make guesses as to what my commands would look like.

Natty Greg

It is for Centos and you're using Centos am I right. so that the step to resize the swap, its a similar for ubuntu, redhat, fedora, mandrake I have checked and everyone uses the same command a little diferent cyntax for different os. This is the one for you.

U_S_A

ASKER

This is what I did

root@cv2 [/home]# cp /etc/fstab /etc/fstab.2017.04.19

root@cv2 [/home]# swapoff /home/swap/systemswap

root@cv2 [/home]# swapoff -a

root@cv2 [/home]# rm /home/swap/systemswap

root@cv2 [/home]# dd if=/dev/zero of=/home/swap/systemswap bs=1024 count=1048576
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 3.31458 s, 324 MB/s

root@cv2 [/home]# mkswap /home/swap/systemswap
mkswap: /home/swap/systemswap: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1, size = 1048572 KiB
no label, UUID=d4786501-508d-4e88-9e3b-406e9d47c828

#in fstab, commented out the UUID line and here is what it looks like now <--
#UUID=3923b91a-942c-4283-8597-85d63514e29e swap swap pri=0,defaults 0 0

#left this line alone
/home/swap/systemswap swap swap defaults,noatime 0 0

root@cv2 [/home]# swapon /home/swap/systemswap

root@cv2 [/home]# grep SwapTotal /proc/meminfo
SwapTotal: 1048568 kB

root@cv2 [/home]# free -m
total used free shared buffers cached
Mem: 112885 93393 19491 5839 3542 13127
-/+ buffers/cache: 76723 36161
Swap: 1023 0 1023

all done

Thanks for the help

U_S_A

ASKER

Thank you.

arnold

Without limiting the swap file size, the growth of the swap file you had before will occur again.