If there are no free partitions on a disk, you can create a swap file. Here is how you add a 12GB file.
# Check what you have for swap. We have one 4GB swap partition.
server# swapon -s
Filename Type Size Used Priority
/dev/mapper/vg_root-lv_swap partition 4194296 0 -1
# Create a 12GB swap file
server# dd if=/dev/zero of=/swapfile bs=1024 count=$((12*1024))k
12582912+0 records in
12582912+0 records out
12884901888 bytes (13 GB) copied, 40.9898 seconds, 314 MB/s
# Check the size with ls.
server# ls -lh /swapfile
-rw-r–r– 1 root root 12G Jan 23 16:47 /swapfile
server# mkswap /swapfile
Setting up swapspace version 1, size = 12884897 kB
# Activate the swap file with a low priority, you don’t really want to use it.
server# swapon -p 9 /swapfile
server# swapon -s
Filename Type Size Used Priority
/dev/mapper/vg_root-lv_swap partition 4194296 0 -1
/swapfile file 12582904 0 9
# If you want it to survive after reboot, at it to the /etc/fstab.