Action

setuid and setgid shell scripts use the file descriptors in /dev/fd. The contents of /dev/fd are a file descriptor file system (FDFS) and have no connection with floppy disks!

Ensure that the fdfs is mounted as /dev/fd. Before the machine is next rebooted, the following line should appear in /etc/vfstab, exactly like this (with no initial comment symbol):

fd		-		/dev/fd		fd	-	no	-

It might be possible to remount /dev/fd without rebooting by running the following as root:

# mount fd /dev/fd

Some administrators, unaware of what /dev/fd is for, comment out the entry in /etc/vfstab that mounts the FDFS (file descriptor file system). This can go unnoticed until an attempt is made to run a setuid or setgid shell script.