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What's the difference between the output of 

cat /proc/sys/fs/inode-nr

and

df -i

Both are documented at returning the number of inodes in use, but they return apparently unrelated numbers.

$ df -i
Filesystem      Inodes  IUsed   IFree IUse% Mounted on
devtmpfs        954448    464  953984    1% /dev
tmpfs           956943      1  956942    1% /dev/shm
/dev/xvda1     1310720 272395 1038325   21% /
/dev/xvdb1     1966080  26278 1939802    2% /tmp
tmpfs           956943      1  956942    1% /hdd1/mnt/data
$ cat /proc/sys/fs/inode-nr
199563      122925
puzzled
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1 Answers1

2

/proc/sys/fs/inode-nr shows data about inodes in RAM (kernel cache), first currently allocated ones, and then free ones. The kernel uses inodes for many things, not just files. For example, network sockets are identified by inodes too.

See https://www.kernel.org/doc/Documentation/sysctl/fs.txt :

The file inode-nr contains the first two items from inode-state, so we'll skip to that file...

Inode-state contains three actual numbers and four dummies. The actual numbers are, in order of appearance, nr_inodes, nr_free_inodes and preshrink.

Nr_inodes stands for the number of inodes the system has allocated, this can be slightly more than inode-max because Linux allocates them one pageful at a time.

Nr_free_inodes represents the number of free inodes (?) and preshrink is nonzero when the nr_inodes > inode-max and the system needs to prune the inode list instead of allocating more.

df -i shows inodes on disk, so whatever each filesystem manages to do with its specific set of inodes.

So both sets of numbers will always remain unrelated to each other.

Patrick Mevzek
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