J&S Marketing

Posted: **January 5th, 2023, 9:19 pm**

Empowering Mail Server and slightly surreal Exim performance

Few years ago...
My mail server Tweaked with Preserving the RAM disk through a Reboot.

Sometimes a server has to be shut down for servicing and you don't want to lose the email in the ram disk spool.
Here's a simple (Red Hat Linux-flavoured) script,
"exim-save", that I've installed as a service that backs up the queue to hard disk and restores it upon reboot.

Code: Select all

nano /etc/init.d/exim-save

Add the line with this:

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# Preserving the RAM disk through a Reboot
# exim-save    
# This shell script takes care of starting and stopping exim
#
# chkconfig: 2345 79 31
# description: Exim Save Data
# Source function library.
./etc/init.d/functions
[ -f /usr/sbin/exim ] || exit 0
start() {      
touch /var/lock/subsys/exim-save       
if [ -d /var/spool/exim-backup ]      
then          
cp -a /var/spool/exim-backup/* 
/var/spool/exim/           
rm -Rf /var/spool/exim-backup        
fi
}
stop() 
{        
rm -f /var/lock/subsys/exim-save       
if ! [ -d /var/spool/exim-backup ]        
then          
rm -Rf /var/spool/exim/db          
rm -Rf /var/spool/exim/scan          
rm /var/spool/exim/*.pid          
cp -a /var/spool/exim 
/var/spool/exim-backup          
rm -Rf /var/spool/exim/input        
fi
}
restart() 
{       
stop       
start
}
# See how we were called.
case "$1" in 
start)       
start       
;;
  stop)        
stop        
;;
  restart)        
restart        
;;
  *)       
echo $
"Usage: $0 {start|stop|restart}"       
exit 
1
esac
exit $RETVAL

I've installed it in the /etc/init.d/exim-save directory as a service and activate it by running:

Code: Select all

chkconfig exim-save on

And Now...

A Better Solution is... tmpfs

Instead of using a ramdisk, rather use tmpfs, supported by Linux kernel 2.4 and up.
The benefit of using tmpfs is... that memory is dynamically assignable, making it a far more flexible solution than ramdisks.
Additionally...
If your tmpfs partition runs out of space, the kernel will automatically begin paging data to your hard disk,
whereas the ramdisk solution would simply cause Exim to stop processing messages and crash.

Using tmpfs, you won't need to do any of the of the steps required for the above ramdisk solution.
The following steps are required for a successful tmpfs configuration:

Create a mountpoint and set correct permissions:

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mkdir /mnt/tmpfs
chown -R mailnull:mail /mnt/tmpfs

Next, open your /etc/fstab file and set the tmpfs partition to be created and mounted at boot:

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#<fs>       <mountpoint>        <type>       <opts>                             <dump/pass>
tmpfs       /mnt/tmpfs          tmpfs        size=1G,nr_inodes=10k,mode=0700    0 0

This will create a 1GB tmpfs partition with 10'000 inodes.
The exim configuration is the same as when creating a ramdisk - either tell Exim that the location of the new spool directory is located at:
/mnt/tmpfs
or
bind the existing spool directory to the mountpoint:
/mnt/tmpfs

Alternatively, you could just mount the tmpfs partition onto Exim's existing spool directory right from the start - so instead of the above changes to the /etc/fstab file, use this line instead:

Next, open your /etc/fstab file and set the tmpfs partition to be created and mounted at boot:

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#<fs>       <mountpoint>        <type>      <opts>                             <dump/pass>
tmpfs       /var/spool/exim      tmpfs      size=1G,nr_inodes=10k,mode=0700    0 0

or

Code: Select all

#<fs>       <mountpoint>        <type>      <opts>                             <dump/pass>
tmpfs       /var/spool/exim      tmpfs      size=2G,nr_inodes=1024k,mode=0700  0 0

Checked within 103 RBL's
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