Archive for December, 2009

Update $DISPLAY in Screen

December 12th, 2009 Comments off

I’ve been a heavy user of GNU Screen for a number of years.  My typical usage is to start a single screen session and attach to it as I move to different computers, either locally or via SSH.  At times I have a need to run X applications from a shell within screen, but with $DISPLAY set to the value screen was initially run with, this tends to not work after it is detached and attached to from a different location.

A few days ago, I came across allsh, a program that allows commands to be executed in all currently running shells.

I was curious if a similar method might work to fix my $DISPLAY issue.  Ideally, I wanted to be able to attach to the screen session from any location and have $DISPLAY updated in all of the bash subprocesses of screen to properly reflect the desired display.

The following is what I came up with to achieve this.

In ~/.profile:

 [ -f ~/.screen-display ] && . ~/.screen-display


# set the $DISPLAY variables if the shell is a child of screen
if [ "`ps -p $PPID -o comm | tail -1`" == "screen" ] ; then
 [ -f ~/.screen-display ] && . ~/.screen-display

And in a file named attach, placed somewhere in your $PATH:


echo "DISPLAY=\"$DISPLAY\"" > ~/.screen-display
echo "SSH_CLIENT=\"$SSH_CLIENT\"" >> ~/.screen-display
echo "SSH_CONNECTION=\"$SSH_CONNECTION\"" >> ~/.screen-display
echo "SSH_TTY=\"$SSH_TTY\"" >> ~/.screen-display
echo "XAUTHORITY=\"$XAUTHORITY\"" >> ~/.screen-display

# detect the pid of screen, but should be smarter if more than one
# instance is running
if [ `screen -ls | awk -F. '/tached/ { print $1 }' | wc -l` != "1" ] ; then
 echo "Unable to detect the desired screen session."
 exit 1
SCREEN_PID=`screen -ls | awk '/tached/ { split($1, a, "."); print a[1] }'`

# find the pids of the shells that are children of screen
BASH_PIDS=`ps -e -o pid,ppid,comm | \
 awk '$2 == var1, $3 ~ /bash/ { print $1 }' var1=$SCREEN_PID`

exec screen -d -r

With this setup, start screen as normal, and then to attach to it from another location, run attach.

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Samba shadow_copy2 Enhancements

December 2nd, 2009 Comments off

A few weeks ago there was a thread on the Samba mailing list regarding some difficulties in getting my shadow copy patches to work with newer versions of Samba.  These patches were originally written for Samba 3.0.25, and since then, Samba has moved up to version 3.4.3, with the 3.5.0 release on the horizon.  The more recent Samba versions also include a shadow_copy2 module that will likely be replacing the shadow_copy module in the future.

I spent some time today adapting the original patches to the shadow_copy2 module.  This patch was made against Samba 3.4.3, and I will be working on a version for Samba 3.5.x over the next couple days.  I hope to get this integrated into Samba, but for now, it’s available below:

Creating a patched Samba source tree can be done with:

$ gzcat samba-3.4.3.tar.gz | tar -xf -
$ cd samba-3.4.3
$ gzcat ../samba-3.4.3-shadowcopy.patch.gz | patch -p1

The parameters added with this patch, as shown at the top of the source file, are:

shadow:sort = asc/desc, or blank for unsorted (default)

This is an optional parameter that specifies that the shadow
copy directories should be sorted before sending them to the
client.  This is beneficial for filesystems that don't read
directories alphabetically (e.g. ZFS).  If enabled, you typically
want to specify descending order.

shadow:format = <format specification for snapshot names>

This is an optional parameter that specifies the format
specification for the naming of snapshots.  The format must
be compatible with the conversion specifications recognized
by str[fp]time.  The default value is "@GMT-%Y.%m.%d-%H.%M.%S".

shadow:localtime = yes/no (default is no)

This is an optional parameter that indicates whether the
snapshot names are in UTC/GMT or the local time.

Example usage with ZFS for the [homes] share is:

   comment = Home Directories
   browseable = no
   writable = yes
   vfs objects = shadow_copy2
   shadow: snapdir = .zfs/snapshot
   shadow: sort = desc
   shadow: localtime = yes
   shadow: format = %Y%m%d-%H%M%S

Where the snapshots would be taken with:

# zfs snapshot -r tank/home@`date +%Y%m%d-%H%M%S`

Recent versions of OpenSolaris allow ZFS snapshots to be created remotely over SMB/CIFS by simply creating a directory in the .zfs/snapshot subdirectory.  To see how this can be used, see my Windows Backups to ZFS post.  Though referring to the SMB/CIFS server built into OpenSolaris, the concept works equally as well with Samba and the shadow copy patch.

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