Here's a procedure how you can add additional swap space to a running RHEL system.

This procedure assumes you will want to add 8 Gigabytes of swap space, and we will be using LVM to do so. To get information from Red Hat on recommended swap space sizes, take a look here: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/ch-swapspace.html.

First start by checking what the current swap space size is, by using the free command:

# free -m -t
             total       used       free     shared    buffers     cached
Mem:        129013     124325       4688          9        173      97460
-/+ buffers/cache:      26691     102322
Swap:        16383       8057       8326
Total:      145397     132382      13015

This particular system has 16 GB of swap space (look in the "total" column next to "Swap:"). Using the -m option with the free command displays the memory values in megabytes. Using the -t option will provide the totals.

You can also see that the system has used 8057 MB of it's swap space, almost half of the swap space available.

Then, figure out how the current swap spaces are configured now:

# cat /proc/swaps
Filename                         Type            Size    Used    Priority
/dev/dm-1                        partition       8388604 8262740 -1
/dev/dm-8                        partition       8388604 0       -2

This shows that there are 2 paging spaces of 8 GB each. To increase the swap space on the system, we'll add another swap space of 8 GB, so the total swap space will go up to 24 GB.

To get a view of what logical volumes exist on the system, use the dmsetup command:

# dmsetup ls
rootvg00-optlv00        (253:7)
rootvg00-tmplv00        (253:3)
rootvg00-varlv00        (253:2)
rootvg00-homelv00       (253:6)
rootvg00-rootlv00       (253:0)
rootvg00-usrlocallv00   (253:5)
rootvg00-swaplv01       (253:8)
rootvg00-usrlv00        (253:4)
rootvg00-swaplv00       (253:1)

This shows that there are 2 logical volumes, swaplv00, and swaplv01. We'll create swaplv02 as the third swap space on the system.

Another good way to see the same information, is by using the lvs command:

# lvs 2>/dev/null
  LV           VG       Attr       LSize
  homelv00     rootvg00 -wi-ao---- 10.00g
  optlv00      rootvg00 -wi-ao----  8.00g
  rootlv00     rootvg00 -wi-ao----  2.00g
  swaplv00     rootvg00 -wi-ao----  8.00g
  swaplv01     rootvg00 -wi-ao----  8.00g
  tmplv00      rootvg00 -wi-ao----  5.00g
  usrlocallv00 rootvg00 -wi-ao----  1.00g
  usrlv00      rootvg00 -wi-ao----  5.00g
  varlv00      rootvg00 -wi-ao----  4.00g

This gives you the information that the logical volumes have been created in the rootvg00 volume group. We'll create the new swap space in the same volume group, using the lvcreate command:

# lvcreate -n swaplv02 -L 8G rootvg00
  Logical volume "swaplv02" created

Using the -n option of the lvcreate command, you can specify the name of the logical volume. The -L option specifies the size (in this case 8G), and you end the command with the volume group name.

Next, you'll have to tell RHEL that the new logical volume is to be formatted for swap space usage:

# mkswap /dev/rootvg00/swaplv02
Setting up swapspace version 1, size = 8388604 KiB
no label, UUID=c9be43f7-c473-45ae-ba13-c1e09af2d95e

Then, you'll have to add an entry to /etc/fstab, so the system knows to re-use the swap space after a system reboot:

# grep swap /etc/fstab
/dev/mapper/rootvg00-swaplv00 swap     swap    defaults        0 0
/dev/mapper/rootvg00-swaplv01 swap     swap    defaults        0 0
/dev/mapper/rootvg00-swaplv02 swap     swap    defaults        0 0

Finally, activate the new swap space using the swapon command:

# swapon -v /dev/rootvg00/swaplv02 swapon on /dev/rootvg00/swaplv02 swapon: /dev/mapper/rootvg00-swaplv02: found swap signature: version 1, page-size 4, same byte order swapon: /dev/mapper/rootvg00-swaplv02: pagesize=4096, swapsize=8589934592, devsize=8589934592

To validate that the new swap space is available on the system, use the free command again, and you may also review /proc/swaps:

# free -m -t
             total       used       free     shared    buffers     cached
Mem:        129013     121344       7669          9        175      95575
-/+ buffers/cache:      25593     103420
Swap:        24575       8109      16466
Total:      153589     129453      24136
# cat /proc/swaps
Filename                         Type            Size    Used    Priority
/dev/dm-1                        partition       8388604 8303856 -1
/dev/dm-8                        partition       8388604 0       -2
/dev/dm-9                        partition       8388604 0       -3

That's it; you're done!



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