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Old 03-18-2009, 06:16 PM   #1
MQMan
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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.
 
Old 03-19-2009, 03:56 PM   #2
allanf
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Quote:
Originally Posted by MQMan View Post
/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.
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.
 
Old 03-22-2009, 11:58 AM   #3
guanx
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/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.
 
Old 03-22-2009, 01:49 PM   #4
gnashley
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Registered: Dec 2003
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Distribution: Slackware
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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.
 
  


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