5

when I tried $ mount command on my system (14.04 LTS), I found some of the results like...

none on /sys/fs/cgroup type tmpfs (rw)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
none on /run/shm type tmpfs (rw,nosuid,nodev)
none on /run/user type tmpfs (rw,noexec,nosuid,nodev,size=104857600,mode=0755)
none on /sys/fs/pstore type pstore (rw)

I am not getting this file system or device node none is mounted on multiple mount points like(/sys/fs/cgroup ,/sys/kernel/security, /run/shm etc)..

does it infer there is nothing or is it a file system or device node..?

6

Usually you mount filesystems which are located on a block device = hard disk, USB stick, ...

Additionally there are some "virtual" file systems such as /proc or /sys which are for interaction with Linux kernel. These do not have any block device associated with them => none is displayed instead.

None is also displayed for tmpfs filesystem. Tmpfs uses RAM for storing temporary files, so there is again no block device associated.

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    thanx @Radek Dostal ,but I have already 'proc' and 'sys' device nodes apart from 'none' --- proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) – lazarus Sep 7 '14 at 10:23
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    I see. I just updated the answer to explain tmpfs. Only things which seems to be missing are debugfs, securityfs, etc. These are similar to sysfs and procfs just expose different things from Linux kernel. – Radek Dostal Sep 7 '14 at 10:28
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    Thanx @ Radek Dostal ,,one more question what does none tmpfs 5.0M 0 5.0M 0% /run/lock none tmpfs 1.5G 42M 1.4G 3% /run/shm none tmpfs 100M 60K 100M 1% /run/user in $ df - Th command means ,,,is it describing about all " virtual " file systems ? – lazarus Sep 7 '14 at 10:38
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    When creating a tmpfs you specify its maximum size. For example 5MB as in the case of /run/lock. This is usually decided by distribution. The rest of the value is quite standard: How much space is actually used, how much is available (compare to maximum limit) and the percentage use. Also be aware that you can create tmpfs which has its limit larger that the amount of RAM you actually have. If you actually use the space, Linux will decided, what will be swapped and in case you will run out of swap even out of memory killer can start killing processes. – Radek Dostal Sep 7 '14 at 10:55

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