Is swap a partition, but not a file system?

Question

Is swap a partition, but not a file system? Is that the reason why df doesn't show it?

Is there a command which can list all the partitions (whether they hold file systems or not)?

Thanks.

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3.9G     0  3.9G   0% /dev
tmpfs           788M  1.5M  786M   1% /run
/dev/sda3       260G   17G  231G   7% /
tmpfs           3.9G  403M  3.5G  11% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/sda4       550G  323G  200G  62% /home
tmpfs           788M   56K  788M   1% /run/user/1000
tmpfs           788M  4.0K  788M   1% /run/user/1001

$ cat /proc/swaps 
Filename                Type        Size    Used    Priority
/dev/sda2                               partition   15625212    12653864    -2

Also, you can use Gparted, a gret application pre-installed in meny Debian distributions. — Z E Nir, Feb 17 '19 at 15:55
@mosvy that is a good answer. It is short, but such is the nature of this question. Please copy to an answer, so we can ✓ you. — ctrl-alt-delor, Feb 17 '19 at 15:57
@ctrl-alt-delor I don't think this question hasn't been answered before. — , Feb 17 '19 at 15:59
you may want to check out kernel.org and the somewhat official description of SWAP, specifically swap management and describing the swap area https://www.kernel.org/doc/gorman/html/understand/index.html — ron, Feb 17 '19 at 23:20

score 3 · Accepted Answer · answered Feb 17 '19 at 16:16

Is swap a partition, but not a file system?

The common way to set up a swap space is indeed to use a partition (like your /dev/sda2). The swap space has some identifiers, so it can be identified as such, but it's not a file system: it doesn't contain files.

You could of course also put swap space on a file on some regular filesystem.

_{(I wouldn't say swap is a partition, but in can lie on a partition.)}

Is that the reason why df doesn't show it?

That, and the fact that df only shows mounted filesystems (visible to the process).

Is there a command which can list all the partitions (whether they hold file systems or not)?

All disk partitioning tools; fdisk, sfdisk, GParted, what have you. They might or might not show what's inside the partitions though. (/proc/partitions also contains a list, but not much details.)

Fabby · Answer 2 · 2019-02-17T19:10:39.857

Is swap a partition, but not a file system?

A swap File / Partition is just a big BLOB where the kernel stores Randomly Accessible Memory. Although RAM can contain files, it needs a RAM DISK conversion to do that.

Is that the reason why df doesn't show it?

Yes, from the man page:

NAME
df - report file system disk space usage

Is there a command which can list all the partitions (whether they hold file systems or not)?

parted --list

Is swap a partition, but not a file system?

2 Answers2