about PATH_MAX: the part of the POSIX standard which determines the maximum number of bytes allowed in an absolute path. In Linux, PATH_MAX is 4096 [src], but it’s possible to construct longer paths if you don’t care about some (most) utilities that use the current working directory to fail due to buffer overflow.
Also, I learned that most filesystems restrict file names to 255 bytes.
What hardlinks are: direct references to inodes. A hardlink can’t reference filesystem objects that don’t have inodes, such as directories or ports, and aren’t portable across different hardware devices even with the same filesystem layout (I think).
Also, the opposite of mount(8) is not unmount, it’s umount >:(
gzip -vt $path_to_file checks the validity of a gzip archive: see
https://unix.stackexchange.com/questions/359303/check-validity-of-gz-file