Bug 9568 - Screen broke
Summary: Screen broke
Alias: None
Product: Red Hat Linux
Classification: Retired
Component: knfsd (Show other bugs)
(Show other bugs)
Version: 6.2
Hardware: i386 Linux
Target Milestone: ---
Assignee: Cristian Gafton
QA Contact:
Depends On:
TreeView+ depends on / blocked
Reported: 2000-02-18 18:46 UTC by Mike Vaillancourt
Modified: 2008-05-01 15:37 UTC (History)
1 user (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2000-02-22 15:24:37 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Mike Vaillancourt 2000-02-18 18:46:37 UTC
After upgrading from Cartman to Piglet screen stopped working if logged in
as a user with the home dir NFS mounted. Any user on the local box and root
worked fine. Had to create a symlink for ~/.screen to point to a local
partition for it to work on NFS mounted home dirs.

Comment 1 Jeff Johnson 2000-02-21 11:11:59 UTC
From Bill Nottingham:
> Someone might want to make sure that the odd files used to multiplex
> screen screens are OK on NFS.

screen uses either named pipes or sockets. Neither work over NFS.

Comment 2 Stephen Tweedie 2000-02-21 20:48:59 UTC
Pipes work fine between compatible implementations.  Most NFSv2 systems use
a way of encoding named pipes as special device files, and if both the client
and server agree on that, named pipes over NFS should work fine.

I've just tried both Cartman and Piglet as both server and client, and named
pipes are still working fine.  Can the user show a "ls -lR" of the faulty
screen directory when things are breaking over NFS?

Comment 3 Bill Nottingham 2000-02-21 21:58:59 UTC
Oops, yeah, Stephen's right. However, the compatible
implementations could be an issue; I've had one report
that it breaks when talking to a Solaris NFS server, for
example. Talking to userland nfsd might also not work;
haven't tried yet.

Comment 4 Mike Vaillancourt 2000-02-21 21:59:59 UTC
ok, I thought I had included the error I got but anyway, here it is. When I
issue screen at the command line I get:

[mikev@mrhat mikev]$ screen
mkfifo /home/support/mikev/.screen/7551.pts-4.mrhat failed
[mikev@mrhat mikev]$

As for the directory:

[mikev@mrhat mikev]$ ls -la .screen/
total 5
drwx------    2 mikev    mikev        1024 Feb 21 17:03 .
drwxr-xr-x   51 mikev    mikev        4096 Feb 21 17:03 ..
[mikev@mrhat mikev]$

Comment 5 Stephen Tweedie 2000-02-21 22:05:59 UTC
Beware --- the NFSv2 standard doesn't support named pipes.  Doing named pipes
requires an incompatible extension to the standard (typically the pipes are
encoded on the wire as a special case of char devices).  All bets are off if
you try passing named pipe inodes over NFSv2.  If it works at all, that's a
bonus, but there's no guarantee especially if client and server are from
different vendors.

Old builds of screen used to create their pipes in /tmp.  Is there any reason
we changed, and do current screen versions have a build option to restore the
old /tmp behaviour?  That would certainly avoid the NFS complication in this

Comment 6 Stephen Tweedie 2000-02-21 22:06:59 UTC
One other question --- I assume it is the client that was upgraded to Piglet,
was it?  What is the server running, and has that changed at all too?

Comment 7 Stephen Tweedie 2000-02-22 14:12:59 UTC
Quick update: 5.2 to 6.1 and 5.2 to 6.2/piglet both work just fine in both
directions.  This is definitely a WORKSFORME unless we can get more information
about the configuration which fails.

Comment 8 Mike Vaillancourt 2000-02-22 14:41:59 UTC
The client was upgraded. The server is running 5.2. These are all internal Red
Hat boxes if you want to look at them.

Comment 9 Bill Nottingham 2000-02-22 14:46:59 UTC
It was changed because in the case where it uses /tmp, it
stores all the screen directories in /tmp/screens; since
it's no longer setuid root, the first person to run
screen gets ownership of the directory. (Plus, it complains
about the permissions on /tmp/screens; it wants it to
be different permissions if screen is run as root.)

Having it put the screens in the users's home directory
works around these issues nicely.

You can, however, still compile it to not do this; there's
a screen-3.9.4-notmp patch in the source RPM; if you don't
apply that patch, it will still use /tmp.OK, so it's the userland NFS server that doesn't support this.
Is supserv running the latest errata nfs-server (in case
this was added at some point past 5.2...)

Comment 10 Stephen Tweedie 2000-02-22 14:47:59 UTC
Which machines are the clients and servers?  I'll go take a look on them.
(Is root available on either of them?)

Comment 11 Stephen Tweedie 2000-02-22 15:24:59 UTC
OK, I've reproduced this on a pure piglet install using the 2.2.15 kernel
version.  Using the kernel from the current tree (2.2.14-3 or later), without
the major NFS changes in the 2.2.15 version we were using before, works just

Upgrade your kernel to the current 6.2 tree and reopen this report if you
still have trouble.

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