Dear Sun Managers,
First off all, thank you to the respondents who,
in according to appearance were:
Brad Young <byoung@splitrock.net>
Jonathan Loh <Jonathan.Loh@bankamerica.com>
Arthur Darren Dunham <add@netcom.com>
Matthew Atkinson <m.atkinson@csl.gov.uk>
Bill Armand <barmand@flash.net>
Kevin Shehan <kevin@joltin.com>
Roger Fujii <rmf@unixbox.lookhere.com>
Jon LaBadie <jon@jgcomp.com>
Most of the respondents (as well as: man 7 tmpfs) noted that
"the tmpfs is a memory based filesystem which uses kernel resources
relating to the VM system and page cache as a filesystem"
So: The short summary is this.
/tmp /tmp is (normally) mounted on a tmpfs file system
tmpfs tmpfs is a "memory based" file system that consists of
physical memory + all available swap space.
Usage for the tmpfs (i.e.; df /tmp) will grows and shrink
according to memory usage on the system.
So if you use alot of disk space under /tmp you have less
swap space for your apps; and if your apps swap alot then
you'll have left disk space in /tmp.
================================
And using my E450 as an example:
->Memory: 1024 MB (See: /usr/platform/`uname -m`/sbin/prtdiag)
->Swap: /dev/md/dsk/d17 is mounted as a tmpfs under /tmp
A swap partition was created on /dev/dsk/c0t0d0s4 at install time.
>From the file: /var/sadm/system/logs/install_log
Physically, this partition is 1000.90MB, which was obtained from:
[root@server] /usr/sbin/format c0t0d0
format> partition
format> print
Part Tag Flag Cylinders Size Blocks
4 swap wu 1452 - 2400 1000.90MB (949/0/0) 2049840
You can list the status of all swap areas with:
[root@server] swap -l
swapfile dev swaplo blocks free
/dev/md/dsk/d17 85,17 16 2049824 1814896
n.b.: The swapfile, /dev/md/dsk/d17 is a meta device which is a
mirror of partitions /dev/dsk/c0t0d0s4 and /dev/dsk/c3t0d0s4
As shown by swap -l the swap partition size is 2049824 512K-blocks,
or 1049509888 bytes (2049824 * 512)
or 1000.89 MB (1049509888 / 1024 / 1024)
which agrees with the output of: format -> partition -> print
(When not under stress) my systems /tmp (tmpfs) typically shows:
[root@server]# df -k /tmp ; echo ; swap -s
Filesystem kbytes used avail capacity Mounted on
swap 1531464 26648 1504816 2% /tmp
total: 280408k bytes allocated + 39336k reserved = 319744k used,
1506896k available
Here df shows 1504816 MB available space which is roughly the
same as the available space reported by swap -s which is
1506896k bytes.
n.b.: Although the man page for tmpfs states that the output of df
may not be accurate, the theoretical maximum size of /tmp is
thus 2.0 GB on my system.
Original question:
On Mon, Jun 21, 1999, Alan Miller wrote:
> Hi David,
>
> Could you, or somebody on the list clarify the statement about
> /tmp, tmpfs, and swap. I've been left alitte confused.
>
> On my Sun E450 /tmp gets mounted via /etc/vfstab which says:
>
> # device device mount FS fsck mount mount
> # to mount to fsck point type pass at boot options
> swap - /tmp tmpfs - yes -
>
> and the command: `df -klt swap` says:
> Filesystem kbytes used avail capacity Mounted on
> swap 1576744 42584 1534160 3% /tmp
>
> What confuses me is your disctinction between tmpfs and swap.
Alan Miller
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