Mount: unknown filesystem type 'swap'

Question

I'm running vanilla Debian Jessie and I need to enable swap file. It works fine when I use swapon /var/swap.img but I'm unable to make it mount with fstab at boot time.

The following entry in fstab:

/var/swap.img none swap sw 0 0

Gives this error:

Error mounting none: mount: unknown filesystem type 'swap'

What is the proper way to mount swap file on Debian with fstab?

[Update]

Adding all entries from fstab:

root@test:~# grep -v "#" /etc/fstab 
UUID=lorem-ipsum / ext4 errors=remount-ro 0 1
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0
/var/swap.img none swap sw 0 0

Output from df:

root@test:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        20G  2.9G   16G  16% /
udev             10M     0   10M   0% /dev
tmpfs            99M  8.4M   91M   9% /run
tmpfs           248M     0  248M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           248M     0  248M   0% /sys/fs/cgroup

Also output from ls:

root@test:~# ls -lh /var/swap.img 
-rw------- 1 root root 1000M Dec 16 17:55 /var/swap.img

I've also checked man and it's not listing swap as supported filesystem type. I'm confused (is this normal?):

adfs, affs, autofs, btrfs, cifs, coda, coherent, cramfs, debugfs, devpts, efs, ext, ext2, ext3, ext4, hfs, hfsplus, hpfs, iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc, qnx4, ramfs, reiserfs, romfs, squashfs, smbfs, sysv, tmpfs, ubifs, udf, ufs, umsdos, usbfs, vfat, xenix, xfs, xiafs.

Solution

You don't mount the swap partition or swapfile with mount, you use the swapon command. (The swap partition or file isn't really a filesystem that can be mounted and hold files, it's an area of the disk the kernel uses directly).

swapon -a will enable all swaps from /etc/fstab.

Comments

[Zoredache]

That looks like a valid line. My functioning jessie system has this. /swapfile1 none swap sw 0 0 Can you show us the full fstab? Is /var on a separate filesystem? Is your swap listed last?

[SiliconMind]

@Zoredache I've updated my question with relevant information. As you can see the /var is on root filesystem.

[unforgettableidSupportsMonica]

swap.img is a silly name for a swapfile, since it's not a disk image. Instead, consider swap.swp or swap.dat or swapfile.

[SiliconMind]

Thanks. Having swap in fstab is what caused my confusion. I just wanted to test if the fstab entry for swap is correct, so obvious choice for me was to use mount. Apparently I was wrong.