perw@holtec.se (Per Westerlund) (02/10/89)
Using SunOS 4.0 (4.0.1) there is available a so called "loopback virtual file system", lofs. The use of it is not apparent, but I would like to use it to mount /var/tmp on /tmp, increasing the apparent size of /tmp, without increasing the true size of the root partition. (Replacing /tmp with a symbolic link to /var/tmp is not acceptable, makes single-user mode without /var mounted a bit hard.) All that should be needed is to add the following line to the config-file options LOFS and make a new kernel. The file-system type is 'lo', and trial runs work, mount -t lo /var/tmp /tmp gives the desired result. Next step is to modify /etc/fstab and /etc/rc to have this mounting automatic. Add the line /var/tmp /tmp lo rw 0 0 to /etc/fstab. Since I have looked at how this is done on the 386i, I add a line to /etc/rc to make it look like this: mount -at 4.2 >/dev/console 2>&1 mount -at lo >/dev/console 2>&1 THIS DOES NOT WORK! During startup this message appears: "mount: unknown filesystem type: lo" but the same command works as long as it is not run from within /etc/rc (by init?). A few possible explanations have been tried, without success: - /etc/mount is statically linked. - /sbin/mount is identical to (/usr)/etc/mount. I have not been able to follow /etc/mount's doings with trace(1), since it does a fork(2), and I loose it. Debugging with adb(1) without a symbol table is so hard that I wont even think about it. Ideas, someone? Per Westerlund Holistic Technology AB Gothenburg SWEDEN +46 31 420370 perw@holtec.se
bukys@cs.rochester.edu (Liudvikas Bukys) (02/16/89)
In article <677@holtec.se> perw@holtec.se (Per Westerlund) writes: >Using SunOS 4.0 (4.0.1) there is available a so called "loopback virtual >file system", lofs....I would like to use it to mount /var/tmp on /tmp, >...(Replacing /tmp with a symbolic link to /var/tmp is not acceptable, >makes single-user mode without /var mounted a bit hard.) If that's your only objection to a symbolic link, then, while single-user, with /var UNMOUNTED, do a "mkdir /var/tmp". Then you'll have a small /var/tmp on your root, to use when standalone, and you'll have your large /var/tmp when you go multi-user.
rayan@ai.toronto.edu (Rayan Zachariassen) (02/16/89)
In the root filesystem, create /var/tmp (/var already exists as a mount pt), and make /tmp -> var/tmp. Then remember there might be files in there if you are ever puzzled by some size vs usage discrepancy in / while you have /var mounted.
perw@holtec.se (Per Westerlund) (02/23/89)
Short recapitulation of the problem: Paraphrased, loop-back filesystems (lofs(4)) are for directories what symbolic links are for files. But, I did not succeed in mounting filesystems of type lofs from the /etc/rc script, which always worked from a shell. The solution: The variable PATH is not exported in /etc/rc, add "export PATH" and mounting lofs-type filesystems works. (Aside: Why is PATH not exported? Will I break something when I export it, due to some very subtle interaction?) The explanation of the solution: Whenever /usr/etc/mount encounters a file system type that it does not recognize, it tries to execute a program called '"mount_%s", <file system type>', in this case mount_lo. (This is not documented, I got a suggestion this was the case by Greg Earle, <earle@sun.com>. Thanks, Greg.) There is a program /usr/etc/mount_lo, but /usr/etc/mount did not find it, since it had the default PATH in the environment. If /etc/rc exports its PATH, which contains /usr/etc, /usr/etc/mount will find mount_lo. Per Westerlund Holistic Technology AB Grona Gatan 59 Gothenburg SWEDEN +46 31 420370 perw@holtec.se
joerg@sun.com (Joerg Schilling - H. Berthold AG Berlin) (02/28/89)
/sbin/mount and /usr/etc/mount only know how to deal with the filesystem
types "ufs", "nfs" and "pc". If you specify any other filesystem type, it
calls a program named mount_xxx where xxx is the filesystem type. To
mount any filesystem of type "lo" it generates an arg vector similar to an
struct mntent and then calls the program mount_lo via execlp.
If you want to mount any "lo" filesystems, you schould have
/usr/etc/mount_lo available and /usr/etc in your search path.
Add after the line:
PATH=/bin:/usr/bin:/usr/etc:/usr/ucb
a line :
EXPORT PATH
to the file /etc/rc.local
and your mount will work.
NOTE:
I positively know this for 4.0 and 4.0.1. I hope this will work as well if
you have the NSE extensions for 3.4/5.
J. Schilling
H. Berthold AG
Teltowkanalstr. 1-4
D 1000 Berlin 46
+49 30 7795 - 400
joerg@berthold.de
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