Operation not permitted Cannot delete file

If an illegal file or similar is placed, there may be cases where the placed file cannot be deleted.
This is something that manipulates file attributes other than permissions in Linux's ext2 and ext3 file systems.

# rm -rf ttyload
rm: cannot remove `ttyload': Operation not permitted

# lsattr ttyload 
s---ia------- ttyload

# chattr -ia ttyload
# lsattr ttyload 
s------------ ttyload

# chattr +ia ttyload
# lsattr ttyload 
s---ia------- ttyload

# rm -rf ttyload