adding swap space in Linux. As previously handled, the setting up
of swap on a free disk partition or else a swap file is discussed.
The following details our example host:
HOST: tux PROMPT: tux [0] OS: CentOS 5.4 LinuxPARTITION: If you already have a free partition that isn't currently
in use, adding it as swap space is as simple as:
tux [0] /sbin/mkswap -v1 /dev/sdc1 Setting up swapspace version 1, size = 536862 kB tux [0] /sbin/swapon -v /dev/sdc1 swapon on /dev/sdc1Since I don't currently have a free partition, I need to create one on
an available disk. The following 'fdisk' command gets us a listing of
our available disks:
tux [0] /sbin/fdisk -l | /bin/grep ^Disk Disk /dev/sda: 11.0 GB, 11004805120 bytes Disk /dev/sdb: 11.0 GB, 11005853696 bytes Disk /dev/sdc: 536 MB, 536870912 bytes Disk /dev/sdd: 536 MB, 536870912 bytesI'm not using 'sdc' for anything so we can use it to create a new
partition for our new swap space. We can use 'sfdisk' to destroy any
previous partition tables and create a new one with a single partition
spanning the full disk. (Alternatively, 'fdisk' or 'parted' could also
be used if you are more familiar with either of them.) The first line
of parameters below tells 'sfdisk' to create partition 1, starting at
sector 0, ending at the last available sector, and set the partition
type to Linux swap (82). The next three lines inform 'sfdisk' that
partitions 2 - 4 are not configured. The rest of the details are the
output of 'sfdisk' after the second 'EOF':
tux [0] /sbin/sfdisk /dev/sdc << EOF > 0,,82 > ; > ; > ; > EOF Checking that no-one is using this disk right now ... OK Disk /dev/sdc: 512 cylinders, 64 heads, 32 sectors/track Old situation: Units = cylinders of 1048576 bytes, blocks of 1024 bytes, counting from 0 Device Boot Start End #cyls #blocks Id System /dev/sdc1 0+ 511 512- 524287+ 83 Linux /dev/sdc2 0 - 0 0 0 Empty /dev/sdc3 0 - 0 0 0 Empty /dev/sdc4 0 - 0 0 0 Empty New situation: Units = cylinders of 1048576 bytes, blocks of 1024 bytes, counting from 0 Device Boot Start End #cyls #blocks Id System /dev/sdc1 0+ 511 512- 524287+ 82 Linux swap / Solaris /dev/sdc2 0 - 0 0 0 Empty /dev/sdc3 0 - 0 0 0 Empty /dev/sdc4 0 - 0 0 0 Empty Warning: no primary partition is marked bootable (active) This does not matter for LILO, but the DOS MBR will not boot this disk. Successfully wrote the new partition table Re-reading the partition table ... If you created or changed a DOS partition, /dev/foo7, say, then use dd(1) to zero the first 512 bytes: dd if=/dev/zero of=/dev/foo7 bs=512 count=1 (See fdisk(8).)Another 'sfdisk' invocation verifies the new partition table layout:
tux [0] /sbin/sfdisk -l /dev/sdc Disk /dev/sdc: 512 cylinders, 64 heads, 32 sectors/track Units = cylinders of 1048576 bytes, blocks of 1024 bytes, counting from 0 Device Boot Start End #cyls #blocks Id System /dev/sdc1 0+ 511 512- 524287+ 82 Linux swap / Solaris /dev/sdc2 0 - 0 0 0 Empty /dev/sdc3 0 - 0 0 0 Empty /dev/sdc4 0 - 0 0 0 EmptyWith the new partition created, we need to use 'mkswap' to tell Linux to
set up a swap area on 'sdc1' and use 'swapon' to add the swap space on
'sdc1'. Finally, verify that the new swap space is available to Linux:
tux [0] /sbin/mkswap -v1 /dev/sdc1 Setting up swapspace version 1, size = 536862 kB tux [0] /sbin/swapon -v /dev/sdc1 swapon on /dev/sdc1 before adding: tux [0] /sbin/swapon -s Filename Type Size Used Priority /dev/sda3 partition 1052248 0 -1 tux [0] /bin/cat /proc/swaps Filename Type Size Used Priority /dev/sda3 partition 1052248 0 -1 after adding: tux [0] /sbin/swapon -s Filename Type Size Used Priority /dev/sda3 partition 1052248 0 -1 /dev/sdc1 partition 524276 0 -2To retain the usage of the swap device through a system reboot, update
/etc/fstab as seen below:
tux [0] /bin/grep swap /etc/fstab LABEL=SWAP-sda3 swap swap defaults 0 0 /dev/sdc1 swap swap defaults 0 0SWAPFILE: For the second option, locate an out of the way place on
a filesystem with adequate space for the swap file to reside. For our
purposes, we'll use '/opt/swapfile' for a new 512 MB swap file. To start,
verify that the directory structure exists and the swap file doesn't:
tux [0] [ ! -d /opt ] && /bin/mkdir /opt tux [1] /bin/ls /opt/swapfile /bin/ls: /opt/swapfile: No such file or directoryTo create '/opt/swapfile' at 512 MB, use 'dd':
tux [2] /bin/dd if=/dev/zero of=/opt/swapfile bs=1k count=512k 524288+0 records in 524288+0 records out 536870912 bytes (537 MB) copied, 5.78956 seconds, 92.7 MB/s tux [0] /bin/chown root:root /opt/swapfile tux [0] /bin/chmod 0600 /opt/swapfile tux [0] /usr/bin/du -sh /opt/swapfile 513M /opt/swapfile tux [0] /bin/ls -l /opt/swapfile -rw------- 1 root root 536870912 Jan 6 17:03 /opt/swapfileAfter file creation, we've set up appropriate ownership and permissions
on 'swapfile', then verified our work. As with our swap partition, use
'mkswap' to create the swap area in 'swapfile' and add it using 'swapon'.
Finally, verify it is availble via another 'swapon' command:
tux [0] /sbin/mkswap -v1 /opt/swapfile Setting up swapspace version 1, size = 536866 kB tux [0] /sbin/swapon -v /opt/swapfile swapon on /opt/swapfile tux [0] /sbin/swapon -s Filename Type Size Used Priority /dev/sda3 partition 1052248 0 -1 /dev/sdc1 partition 524276 0 -2 /opt/swapfile file 524280 0 -3To retain the usage of the swap file through a system reboot, update
/etc/fstab as seen below:
tux [0] /bin/grep swap /etc/fstab LABEL=SWAP-sda3 swap swap defaults 0 0 /dev/sdc1 swap swap defaults 0 0 /opt/swapfile swap swap defaults 0 0Should you need to remove the swap space provided by a disk partition
or swap file, 'swapoff' is used:
tux [0] /sbin/swapoff /dev/sdc1 tux [0] /sbin/swapoff /opt/swapfile tux [0] /sbin/swapon -s Filename Type Size Used Priority /dev/sda3 partition 1052248 0 -1Of note, only swap space that isn't in use can be removed.
see also:
Adding Swap Space in FreeBSD
Adding Swap Space in Solaris
