I'm learning about partitioning disks for different server applications, and was exploring mtab to see what sort of partitioning scheme is set up. I'm seeing filesystems that aren't described in /etc/fstab, and beyond being mentioned as an existing type (many aren't even mentioned) aren't described in the man pages. Here's my mtab file:

sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
udev /dev devtmpfs rw,nosuid,relatime,size=8134380k,nr_inodes=2033595,mode=755 0 0
devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /run tmpfs rw,nosuid,nodev,noexec,relatime,size=1634440k,mode=755 0 0
/dev/sdb2 / ext4 rw,relatime,errors=remount-ro 0 0
securityfs /sys/kernel/security securityfs rw,nosuid,nodev,noexec,relatime 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
tmpfs /run/lock tmpfs rw,nosuid,nodev,noexec,relatime,size=5120k 0 0
cgroup2 /sys/fs/cgroup cgroup2 rw,nosuid,nodev,noexec,relatime,nsdelegate,memory_recursiveprot 0 0
pstore /sys/fs/pstore pstore rw,nosuid,nodev,noexec,relatime 0 0
efivarfs /sys/firmware/efi/efivars efivarfs rw,nosuid,nodev,noexec,relatime 0 0
none /sys/fs/bpf bpf rw,nosuid,nodev,noexec,relatime,mode=700 0 0
systemd-1 /proc/sys/fs/binfmt_misc autofs rw,relatime,fd=29,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=11410 0 0
mqueue /dev/mqueue mqueue rw,nosuid,nodev,noexec,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,nosuid,nodev,noexec,relatime 0 0
hugetlbfs /dev/hugepages hugetlbfs rw,relatime,pagesize=2M 0 0
tracefs /sys/kernel/tracing tracefs rw,nosuid,nodev,noexec,relatime 0 0
configfs /sys/kernel/config configfs rw,nosuid,nodev,noexec,relatime 0 0
fusectl /sys/fs/fuse/connections fusectl rw,nosuid,nodev,noexec,relatime 0 0
/dev/sdb6 /home ext4 rw,relatime 0 0
/dev/sdb3 /var ext4 rw,relatime 0 0
/dev/sdb5 /tmp ext4 rw,relatime 0 0
/dev/sdb1 /boot/efi vfat rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0
tmpfs /run/user/1000 tmpfs rw,nosuid,nodev,relatime,size=1634436k,nr_inodes=408609,mode=700,uid=1000,gid=1000 0 0
gvfsd-fuse /run/user/1000/gvfs fuse.gvfsd-fuse rw,nosuid,nodev,relatime,user_id=1000,group_id=1000 0 0
portal /run/user/1000/doc fuse.portal rw,nosuid,nodev,relatime,user_id=1000,group_id=1000 0 0

Some of these I understand, like the /dev/sdx# directory fs entries. But most of the other ones I have no idea about. Particularly, sysfs, proc, devtmpfs, devpts, securityfs, cgroup2, pstore, efivars, autofs, mqueue, debugfs, hugetlbfs, tracefs, configfs, fusectl. What are these filesystem types?

None of these are mentioned in /etc/fstab, so where and when are they mounted?


1 Answer 1


A comment mentions What is /etc/mtab in Linux?, which is appropriate, but the top answer in that question is hard to follow in this context. To summarize that answer's third paragraph: The Linux kernel exposes a number of its internal data structures in the form of files on a file system.

The proc, sysfs, udev, debugfs, tracefs, and other filesystem types you're asking about are pseudo-types involved in exposing the various categories of kernel data as if they are files in trees of subdirectories under the /proc and /sys directories (and perhaps a few others).

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