This column is described in Linux's man fstab as:
The fourth field, (
fs_mntops), describes the mount options associated with the filesystem.It is formatted as a comma separated list of options. It contains at least the type of mount plus any additional options appropriate to the filesystem type. For documentation on the available options for non-nfs file systems, see
mount(8).
When file system is swap, these mount options doesn't do anything. See: What is the difference between swap entries in fstab?
These fstab options are part of struct fstab:
struct fstab { char *fs_spec; /* block special device name */ char *fs_file; /* filesystem path prefix */ char *fs_vfstype; /* type of filesystem */ char *fs_mntops; /* comma separated mount options */ char *fs_type; /* rw, ro, sw, or xx */ int fs_freq; /* dump frequency, in days */ int fs_passno; /* pass number on parallel fsck */ }; So in summary there are 6 columns in /etc/fstab means:
fs_spec: describes the block special device, the local filesystem, or the remote filesystem to be mounted.fs_file: describes the mount point for the filesystem. For swap partitions, this field should be specified asnone.fs_vfstype: describes the type of the filesystem.fs_mntops: describes the mount options associated with the filesystem.fs_freq: is used for these filesystems by thedumpcommand to determine which filesystems need to be dumped.fs_passno: is used by thefsckprogram to determine the order in which filesystem checks are done at reboot time.