How to Create a Swap File and Make It Available

1. Become superuser.

   You can create a swap file without root permissions. However, to avoid accidental overwriting, root should be the owner of the swap file.

2. Create a directory for the swap file, if needed.

3. Create the swap file.

   # mkfile nnn[k|b|m] filename

   
   

   The swap file of the size nnn (in Kbytes, bytes, or Mbytes) and filename you specify is created.

4. Activate the swap file.

   # /usr/sbin/swap -a /path/filename

   
   

   You must use the absolute path name to specify the swap file. The swap file is added and available until the file system is unmounted, the system is rebooted, or the swap file is removed. Keep in mind that you can't unmount a file system while some process or program is swapping to the swap file.

5. Add an entry for the swap file to the /etc/vfstab file that specifies the full path name of the file, and designates swap as the file system type, as follows:

   /path/filename - - swap - no -

   
   

6. Verify that the swap file is added.

   $ /usr/sbin/swap -l

   
   

Example--Creating a Swap File and Making It Available

The following examples shows how to create a 100-Mbyte swap file called /files/swapfile.

# mkdir /files
# mkfile 100m /files/swapfile
# swap -a /files/swapfile
# vi /etc/vfstab
(An entry is added for the swap file):
/files/swapfile   -      -       swap     -     no     -
# swap -l
swapfile             dev  swaplo blocks   free
/dev/dsk/c0t0d0s1   136,1      16 1638608 1600528
/files/swapfile        -       16 204784  204784

Removing a Swap File From Use

If you have unneeded swap space, you can remove it.

How to Remove Unneeded Swap Space

1. Become superuser.

2. Remove the swap space.

   # /usr/sbin/swap -d /path/filename

   
   

   The swap file name is removed so that it is no longer available for swapping. The file itself is not deleted.

3. Edit the /etc/vfstab file and delete the entry for the swap file.

4. Recover the disk space so that you can use it for something else.

   # rm /path/filename

   
   

   If the swap space is a file, remove it. Or, if the swap space is on a separate slice and you are sure you will not need it again, make a new file system and mount the file system.

   For information on mounting a file system, see Chapter 40, Mounting and Unmounting File Systems (Tasks).

5. Verify that the swap file is no longer available.

   # swap -l

   
   

Example--Removing Unneeded Swap Space

The following examples shows how to delete the /files/swapfile swap file.

# swap -d /files/swapfile
# (Remove the swap entry from the /etc/vfstab file)
# rm /files/swapfile
# swap -l
swapfile             dev  swaplo  blocks   free
/dev/dsk/c0t0d0s1   136,1      16 1638608 1600528