25.2.2.3 Inode problems
The UNIX filesystem uses inodes to store information about files. One way to make the disk unusable is to consume all of the free inodes on a disk, so no new files can be created. A person might inadvertently do this by creating thousands of empty files. This can be a perplexing problem to diagnose if you're not aware of the potential because the df command might show lots of available space, but attempts to create a file will result in a "no space" error. In general, each new file, directory, pipe, FIFO, or socket requires an inode on disk to describe it. If the supply of available inodes is exhausted, the system can't allocate a new file even if disk space is available.
You can tell how many inodes are free on a disk by issuing the df command with the -i option:
% df -o i /usr >may be df -i on some systems
Filesystem iused ifree %iused Mounted on
/dev/dsk/c0t3d0s5 20100 89404 18% /usr
%
The output shows that this disk has lots of inodes available for new files.
The number of inodes in a filesystem is usually fixed at the time you initially format the disk for use. The default created for the partition is usually appropriate for normal use, but you can override it to provide more or fewer inodes, as you wish. You may wish to increase this number for partitions in which you have many small files - for example, a partition to hold Usenet files (e.g., /var/spool/news). If you run out of inodes on a filesystem, about the only recourse is to save the disk to tape, reformat with more inodes, and then restore the contents.
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