Você precisa disso:
x /tmp/foo - - - - -
Mas observe isto:
Note that lines of this type do not influence the effect of r or R lines.
página man:
r
Remove a file or directory if it exists. This may not be used to remove non-empty directories, use R for that. Lines of this type accept shell-style globs in place of normal path names. Does not follow symlinks.
R
Recursively remove a path and all its subdirectories (if it is a directory). Lines of this type accept shell-style globs in place of normal path names. Does not follow symlinks.
x
Ignore a path during cleaning. Use this type to exclude paths from clean-up as controlled with the Age parameter. Note that lines of this type do not influence the effect of r or R lines. Lines of this type accept shell-style globs in place of normal path names.
The configuration format is one line per path containing type, path, mode, ownership, age, and argument fields:
#Type Path Mode UID GID Age Argument
d /run/user 0755 root root 10d -
L /tmp/foobar - - - - /dev/null
Fields may be enclosed within quotes and contain C-style escapes.