There are several ways, a filesystem can be used to introduce nondeterminism:

1. readdir order is already covered in its own section

2. storing mtime, ctime or atime values of files touched during build will introduce varying timestamps

3. using st_ino or st_dev fields from stat(2)

4. storing st_size for directories or using st_blocks or st_blksize for any file, because it is filesystem-dependent. E.g. creating a million files and removing them again, will cause a directory to be large on ext4

Seen in the wild:

1. • see readdir
2. • .pyc files in cpython
   • compiled free pascal (fpc) files
   • fwnn .dic files
3. • fwnn
   • geany
4. • rpm