LinuxQuestions.org - Filesystem for /dev

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Filesystem for /dev

/dev now uses the tmpfs filesystem. How come it doesn't show up in df:

Code:

eddie@Slacker:~$ cat /proc/mounts

rootfs / rootfs rw 0 0

/dev/hda2 / xfs rw,attr2,nobarrier,noquota 0 0

/proc /proc proc rw 0 0

sysfs /sys sysfs rw 0 0

tmpfs /dev tmpfs rw,mode=755 0 0

devpts /dev/pts devpts rw,gid=5,mode=620 0 0

usbfs /proc/bus/usb usbfs rw 0 0

/dev/hda1 /boot ext2 rw,errors=continue 0 0

tmpfs /dev/shm tmpfs rw 0 0



eddie@Slacker:~$ df -h -a

Filesystem            Size  Used Avail Use% Mounted on

/dev/hda2            9.6G  2.7G  7.0G  28% /

/proc                    0    0    0  -  /proc

sysfs                    0    0    0  -  /sys

usbfs                    0    0    0  -  /proc/bus/usb

/dev/hda1              15M  6.6M  7.5M  47% /boot

tmpfs                506M    0  506M  0% /dev/shm

Also, a new Slack install of 12.2 has the following in /etc/fstab:

Code:

tmpfs /dev/shm tmpfs defaults 0 0

But that entry is missing in my 12.0 -> 12.1 -> 12.2 system. Should I add it to my "upgraded" system. Or, indeed, is it ever needed at all, as it's mounting a tmpfs filesystem to another tmpfs filesystem.

Cheers.

Quote:

Originally Posted by MQMan (Post 3479969)

/dev now uses the tmpfs filesystem. How come it doesn't show up in df:

Code:

eddie@Slacker:~$ cat /proc/mounts

rootfs / rootfs rw 0 0

/dev/hda2 / xfs rw,attr2,nobarrier,noquota 0 0

/proc /proc proc rw 0 0

sysfs /sys sysfs rw 0 0

tmpfs /dev tmpfs rw,mode=755 0 0

devpts /dev/pts devpts rw,gid=5,mode=620 0 0

usbfs /proc/bus/usb usbfs rw 0 0

/dev/hda1 /boot ext2 rw,errors=continue 0 0

tmpfs /dev/shm tmpfs rw 0 0



eddie@Slacker:~$ df -h -a

Filesystem            Size  Used Avail Use% Mounted on

/dev/hda2            9.6G  2.7G  7.0G  28% /

/proc                    0    0    0  -  /proc

sysfs                    0    0    0  -  /sys

usbfs                    0    0    0  -  /proc/bus/usb

/dev/hda1              15M  6.6M  7.5M  47% /boot

tmpfs                506M    0  506M  0% /dev/shm

Also, a new Slack install of 12.2 has the following in /etc/fstab:

Code:

tmpfs /dev/shm tmpfs defaults 0 0

The 'df' command walks through the mount point table and reports on "mounted" partitions only. The "/dev" is not mounted as the contents are drivers for the hardware and not storage.

/etc/mtab does not contain all mounted devices but only the ones intended for normal users to see. You can see /proc/mounts for a complete list.

guanx is correct -when /dev gets mounted on tmpfs the mount command uses the '-n' option which causes it to be mounted without creating an entry in /etc/mtab.