Monthly Archives: August 2016

CLI

Mountpoint check script

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I wrote a simple script to check to see if a specific mountpoint on a Linux system is still live.  It does this by trying to read a specific file on the share, and if it cannot, write the event to a log, unmount, and then re-mount the folder. The need arose for instances where a file server has been rebooted and the linux system loses the connection to the share. This way it will automatically re-mount.

Modify the variables section as needed and then have a cron job run the script as root at whatever interval you want. Enjoy.

#!/bin/bash
#Script to monitor mount directories to ensure they are properly mounted
#Place a file with the word "mounted" in it inside all mounted directories
#The script will try to read the file and attempt to unmount and remount the folder if it fails to read the file
#Updated 8/30/2016 by Nicholas Jeppson

#---------Variable section------------#

#Place mount folder locations here, separated by space 
#Paths containing spaces need to have quotes around them
LOCATIONS=(/home/njeppson /home/njeppson/Desktop)

#Name of file to try to read
TEST_FILENAME="mountcheck"

#---------End Variable Section--------#
#-----Do not edit below this line-----#

#Read file, if contents don't contain "mounted" then attempt to unmount and re-mount the folder, output attempt to /var/log/mountcheck

for FOLDER in "${LOCATIONS[@]}"; do 
 if [[ $(cat $FOLDER/$TEST_FILENAME) != "mounted" ]]; then
 echo "$(date "+%b %d %T") $(hostname) $FOLDER Not mounted, remounting." >> /var/log/mountcheck 
 umount $FOLDER
 mount $FOLDER
 fi
done
Gaming, OS

Battle.net won’t update after copying from network folder

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I ran into an issue recently where I tried to copy a battle.net game (Heroes of the Storm) from a backup folder on my NAS onto a new computer. Once the copy was completed I couldn’t get battle.net to update the game. It kept failing with error code:

BLZBNTAGT00000840

file update failed for an unknown reason.

After much digging I found this post which mentions it’s due to the fact that the updater apparertly can’t update files with the hidden attribute. The hidden file attribute gets applied by the NAS because the file in question has a dot in front of it in the filename. For some reason the updater can’t touch it.

The fix is to change all files in the game folder to not have the hidden attribute. The easiest way to do this is via the command line. Navigate to the folder of the game you copied over and execute the following:

attrib -H .* /S

Finally, I can copy Blizzard game backups without agonizing over why they won’t patch.

CLI, OS, Web

FreeBSD: allow non-root processes to bind port 80

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In experimenting with FreeNAS jails I wanted to allow a web service to use port 80. Normally 80 is a high order port reserved for root-level processes for security reasons. Since this is a FreeBSD jail and not a full on system I’m not worried about this.

The command to do so is fairly simple (thanks to this page for information)

sysctl net.inet.ip.portrange.reservedhigh=0

The above command is not permanent; to make it so add it to /etc/sysctl.conf:

echo "net.inet.ip.portrange.reservedhigh=0" >> /etc/sysctl.conf
CLI, OS

FreeNAS unable to create jails fix

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I recently got a shiny new FreeNAS Mini appliance. It’s the bee’s knees. Previously I was using a virtualized instance of FreeNAS that has served me admirably for two years now. During the migration I decided to start fresh with the jails configuration I had and deleted the entire jails dataset. This turned out to be a mistake. I suddenly found out that I couldn’t create any jails or plugins. The plugin download would hang for a long time and flash a brief message “Failed to download plugin.” Not helpful.

I tried changing the location of my jails in configuration to no avail. I even tried nuking my FreeNAS config entirely and starting from scratch. The error still happened! Somehow that configuration survived a factory restore.

I finally found this freenas forum entry that pointed me in the right direction. It suggested I use the warden command to delete the plugin jail template completely and re-install it. When I tried to I got this error:

 

[nicholas@freenas ~]$ sudo warden template delete pluginjail
ERROR: Not a ZFS volume: /mnt/storage/jails/.warden-template-pluginjail

It was still trying to install the plugin template in my non-existent dataset. I decided to try re-creating the missing dataset and then running the warden delete command again. Success!

[nicholas@freenas ~]$ sudo zfs create storage/jails/.warden-template-pluginjail
[nicholas@freenas ~]$ sudo warden template delete pluginjail

Once you delete the template jail via warden, you can re-create it in the right place after configuring the correct path in Jails / Configuration. Once you have the right place configured, issue the following:

warden template create -nick pluginjail -tar http://download.freenas.org/jails/9.3/x64/freenas-pluginjail-9.3-RELEASE.tgz

Plugins and jails work again! Success.

CLI

The power of find, grep, and xargs

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Recently I needed to find folders with two different things in the path – mysql and DB. I toyed around with a bunch of options but finally settled on using xargs. I don’t use it much. I should use it more.

The command below takes output from find, greps it twice (thus looking for things that have both terms in them) and then creates a symbolic link of the results.

 find . -type d | grep mysql | grep DB | xargs -n 1 ln -s

This accomplished what I needed quite well. In a huge stash of folders there were a subset that contained both the words mysql and DB in their paths that  I was interested in. Find, grep, and xargs to the rescue.

CLI

Grep handy tips

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I found some grep flags that are really handy and wanted to write them down.

Only list exact matches:  -w

When I run the “netstat -an | grep LISTEN” command it would include all text that included LISTEN – including LISTENING, which I didn’t want to see. Appending -w to the netstat command makes sure grep only displays exact matches.

netstat -an | grep -w LISTEN

Include extra lines above and below the match: -A, -B

When administering xenserver systems it’s often useless to use grep defaults because Xen likes to include relevant information on different lines. To fix this, use the -A and/or the -B flags to specify the number of lines after (A) or before (B) to include in the results. A real world example using grep to return the 3 lines above and below the line matching the word Splunk:

xe vdi-list | grep -A3 -B3 Splunk

 

CLI

Embed commands in if statements in bash

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I’ve recently had to do some bash-fu and thought I’d document it in case I come across the need again. It involved an if statement inside a for loop. The if statement looked at the result of an external command and acted if conditions were met.

The scenario: An application created folders beginning with a series of digits.  Later it was decided to add a prefix to new folders. A problem occurred where there were folders with the same numeric sequence – corresponding to the same user – but the program was saving things in both prefixed and non-prefixed folders at random. We needed a way to copy information from the numeric only folders into the prefix folders, then backup and delete the numeric-only folders. We also wanted to be warned about any file overwrites in the process.

After a bunch of research and experimentation I came up with the following one-line bash script:

for d in [0-9]*; do BN=$(basename "$d"); if [[ $(find . -maxdepth 1 -type d -name "*$d" | grep -o $d | wc -l) = 2 ]]; then  cp -i -p -r "$d" ../archive/"$d"; cp -i -p -r "$d"/* "PREFIX_$BN"; rm -rf "$d"; fi; done

It does the following:

  • Scan the current directory for files (or folders) beginning with numbers
  • Save the basename of discovered file to a variable (basename was required to remove the ./ that showed up in the results) and use that variable for the copy command
  • Scans the current directory to see if there is another folder with the same string of numbers in its name (same name but only with a prefix attached)
  • If there is a folder with the same string of numbers in its name, copy the non-prefixed folder to an archive location, then copy its contents to the folder with the prefix, prompting before overwriting anything.
  • Once the copy is complete, delete the original non-prefixed folder

The big learning moment for me was embedding a bash command into an if statement. The if statement runs the find command, pipes to wc -l to count the number of results, and then compares that result to something else. Pretty handy.

Thanks to these sites for helping me in my journey:

If statement inside for loop: https://unix.stackexchange.com/questions/52800/how-to-do-an-if-statement-from-the-result-of-a-executed-command

Find results only in current directory:  https://unix.stackexchange.com/questions/162411/find-maxdepth-0-not-returning-me-any-output

Count results from find command: https://stackoverflow.com/questions/6181324/counting-regex-pattern-matches-in-one-line-using-sed-or-grep

Warn before overwriting files: https://askubuntu.com/questions/236478/how-do-i-make-bash-warn-me-when-overwriting-an-existing-file

CLI

Add prefix to filenames in bash

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A quick handy little way to add a prefix to files in bash (taken from here)

for f in * ; do mv "$f" "PRE_$f" ; done

In my case I wanted to rename all sub-100 filenames to have an extra zero so sorting played nicely with filenames beginning with 100+. To accomplish this I found about the rename command (thanks to this site.)  The command I used to enforce natural sorting was the following:

rename 's/\d+/sprintf("%03d", $&)/e' *

The command looked for anything beginning with a number, then used sprintf to make the number 3 digits. The asterisk instructed the rename command to work on every file. Success.