Why is devfs full?

A simple df -h reports:

Filesystem      Size   Used  Avail Capacity   iused    ifree %iused  Mounted on
/dev/disk0s2   465Gi  201Gi  264Gi    44%  52634885 69251887   43%   /
devfs          180Ki  180Ki    0Bi   100%       622        0  100%   /dev
map -hosts       0Bi    0Bi    0Bi   100%         0        0  100%   /net
map auto_home    0Bi    0Bi    0Bi   100%         0        0  100%   /home

What is devfs & map -hosts & map auto_home?

Why is devfs 100% capacity?

Solution 1:

devfs is a special filesystem containing a representation of physical devices.

The implementation of devfs doesn't maintain file system statistics, like space available (because you can't store anything on devfs), but because devfs is visible as a part of the filesystem hierarchy, it must report those values to the regular tools asking for them. In effect the tools will show the file system space and inode usage as 100%.

Likewise map -hosts and map auto_home are not real file systems, but mountpoints for autofs - a component which automatically mounts external devices and network shares. See man automount and man automountd.