mjhjmtu

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

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.)

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