query on swap entry in the /etc/fstab file

[Md. Minhaz Khan]

Dear all

What is the difference between below two lines in the /etc/fstab file for dev swap:

(1)/dev/vg00/lvol9 . swap defaults 0 0
(2)/dev/vg00/lvol9 ... swap pri=1 0 0

Actually i want to know what is meant by "." and "..." plus "pri=1 0 0" in the /etc/fstab file for device swap??

Thanks in advance

Minhaz

[Steven E. Protter]

Shalom,

the . and ... are placeholders to make the output look good. I'm surprised that didn't make the mount fail. Those are put in manually, not by Ignite system install.

The pri display tells the system if it has two swap areas which has higher priority. This can be used to tune swap performance.

higher priority number makes the swap area less likely to be used.

There is a man page on /etc/fstab that should cover this.

SEP

[johnsonpk]

Hi Minhaz,

You can put any thing like "." or "..."or "/" as the mount point portion can not be blank in the /etc/fstab ,and effectively there is no difference between "." and "..." as it is ignored by swapon command.

pri=1 field is for the priority for allocating the swap device for paging and swapping

The priority ranges are from 0(highest) to 10 and space is taken from lower-numbered system first

Rgds
Johnson

[Md. Minhaz Khan]

hi johnson

Thanks a lot for your reply.

But what is meant by


if i put only "pri=1" then what is it mean??

if i put only "pri=1 0 0" then what is it mean??

Again if we have 4 additional device swap and each has priority "pri=1 0 0" then what is the scenario of paging??

please help me to understood.

Thanks
Minhaz

[johnsonpk · Accepted solution]

>>if i put only "pri=1" then what is it meani

The swap device will have priority 1 (you can see the priority by swapinfo -tam)
>>if i put only "pri=1 0 0" then what is it mean??

The last two digits are for backup frequency and pass number


>>Again if we have 4 additional device swap and each has priority "pri=1 0 0" then what is the scenario of paging??

All the four device have equal priority and ideally all of them will be engaged equally at the the time of paging

backup frequency:

-----------------
Reserved for possible use by future backup utilities.

pass number :
--------------

Used by the fsck command to determine the order in which file system checks are done. The root file system should be specified with a pass number of 1, to be checked first, and other file systems should have larger numbers. (A file system with a pass number of zero is ignored by the fsck command.)

File systems within a drive should be assigned different pass numbers, but file systems on different drives can be checked on the same pass, to utilize possible parallelism available in the hardware. If pass number is not present, fsck checks each such file system sequentially after all eligible file systems with pass numbers have been checked.

Rgds
Johnson

[Md. Minhaz Khan]

Thanks a lot to everybody(specially johnson) for helping me.

Regds
Minhaz