What does "sw" option mean in /etc/fstab?
According to the link below, the 'sw' option indicates that the swap partition is to be activated with 'swapon -a' command:
/dev/hda6 none swap sw 0 0
http://www.linuxquestions.org/questions/linux-newbie-8/fstab-defaults-sets-wrong-permissions-145958/
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 thedump
command to determine which filesystems need to be dumped.fs_passno
: is used by thefsck
program to determine the order in which filesystem checks are done at reboot time.