Re: [uml-devel] When /tmp is not tmpfs.

[Rob Landley <rob@landley.net>]

FYI:

The mounts on a Fedora Core 4 system:

/dev/hda2 on / type ext3 (rw)
/dev/proc on /proc type proc (rw)
/dev/sys on /sys type sysfs (rw)
/dev/devpts on /dev/pts type devpts (rw,gid=5,mode=620)
/dev/hda1 on /boot type ext3 (rw)
/dev/shm on /dev/shm type tmpfs (rw)
/dev/hdb1 on /home type ext3 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
none on /var/named/chroot/proc type proc (rw)
automount(pid1716) on /misc type autofs 
(rw,fd=4,pgrp=1716,minproto=2,maxproto=4)
automount(pid1759) on /net type autofs 
(rw,fd=4,pgrp=1759,minproto=2,maxproto=4)
nfsd on /proc/fs/nfsd type nfsd (rw)

/tmp is nothing special (it inherits / which is ext3), but /dev/shm is a tmpfs 
mount which is world writeable and has the sticky bit set.

The mounts on the x86-64 PLD system I've been borrowing (and on which I do not 
have root access):

/dev/sda3 on / type jfs (rw)
none on /proc type proc (rw,gid=17)
sysfs on /sys type sysfs (rw)
selinuxfs on /selinux type selinuxfs (rw)
/dev/sda1 on /boot type ext2 (rw)
/dev/sda5 on /usr type jfs (rw)
/dev/sda6 on /var type jfs (rw)
/dev/sda7 on /tmp type jfs (rw)
/dev/sda8 on /home type jfs (rw)
/dev/sda9 on /srv type jfs (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
/root/pldcd-0.95.iso on /root/pld type iso9660 (rw,loop=/dev/loop0)

/tmp is an explicit scsi mount.  /dev/shm inherits / (which is jfs), but 
that's moot because the directory is not world writeable.

The shell servers from sourceforge:

/dev/md0 on / type ext3 (rw,errors=remount-ro)
none on /proc type proc (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
usbfs on /proc/bus/usb type usbfs (rw)
/dev/md1 on /tmp type ext3 (rw)
/dev/md2 on /var type ext3 (rw)
/dev/md3 on /usr type ext3 (rw)
/dev/md4 on /var/local type ext3 (rw)
none on /dev/shm type tmpfs (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
pr-fs-users-a:/home/users/a on /home/users/a type nfs 
(rw,nosuid,nodev,nfsvers=3,udp,rsize=16384,wsize=16384,hard,intr,addr=10.5.1.153)
... and so on [about 8 gazillion more /home/users/blah mounts trimmed].

Again, /tmp is not tmpfs (it's ext3 on a raid), but /dev/shm is a tmpfs mount 
which is world writeable and has the sticky bit set.

And I reiterate that on my ubuntu laptop /tmp is not tmpfs (it inherits my 
ext3 /) but /dev/shm is a world writeable tmpfs mount that has the sticky bit 
set.

My conclusion from this is that /dev/shm is probably a better default 
than /tmp for User Mode Linux's physical memory file, perhaps with a fallback 
to /tmp if it can't write there.  But I'd appreciate hearing from other 
people with different systems.

The assumption that tmpfs is already mounted on /tmp does not seem to be true 
on any preexisting system I can currently find out in the field.  Where have 
you seen this?

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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