I assume your friend is using an ext fs, because its one of the few sensible fs that can run out of inodes.
It would appear your friend either fiddled with his filesystem and broke it or has a ridiculously large volume of several TB. Inodes are not a use-once-and-throw away thing. If he really ran out of inodes it means he has ridiculously many files and directories ... which can happen on a >4TB (educated guess) volume, where "only" 700GB are free. For the ext family of fs the number of inodes is determined when the fs is created. From the
mkfs.ext4 man page:
Specify the bytes/inode ratio. mke2fs creates an inode for every bytes-per-inode
bytes of space on the disk. The larger the bytes-per-inode ratio, the fewer inodes
will be created. This value generally shouldn't be smaller than the blocksize of
the filesystem, since in that case more inodes would be made than can ever be used.
Be warned that it is not possible to expand the number of inodes on a filesystem
after it is created, so be careful deciding the correct value for this parameter.
To shorten the remainder of this answer: This means
mkfs is either provided with such a ratio, or it will assume one. If your friend uses the fs differently than assumed the chosen ratio may be wrong for his use case and he gets that error ... filling up a single multi-TB volume with tons of small files may count as such.
Does your friend use some desktop environment that implements the concept of a "trash can" for files or any other forms of backups that may create large amounts of files? Maybe he can fix his problem by simply getting rid of unneeded files.
I remember this issue with ext2 from about the time when kernel 2.4 was fairly new. As a rule of thumb, I always use XFS for volumes that are very large compared to what is currently common. Currently I'd call everything between 250GB to 1TB common for a single volume and we can buy 4TB HDDs. So for everything >3TB I'd rather use XFS than ext. Just a rule of thumb, but haven't run out of inodes for a long time ...