cloud engineer
How to create a swap file.
A 2GB swap file.
dd if=/dev/zero of=/swapfile bs=1k count=2048k |
Activate.
mkswap /swapfile chmod 0600 /swapfile systemctl daemon-reload swapon /swapfile |
To make swap permanent, add to /etc/fstab.
/swapfile swap swap defaults 0 0 |
Check if swap is working.
cat /proc/swaps free -h |
Here’s another way to add startup scripts to your instance during creation.
UserData:
Fn::Base64: !Sub |
#cloud-config
repo_upgrade: none
runcmd:
# Cloud init startup script
- "bash /root/setup.sh"
write_files:
# Cloud init startup script
- owner: root:root
permissions: '0644'
path: /root/setup.sh
content: |
#! /bin/bash -x
write_files:
# Cloud init startup script
- owner: root:root
permissions: '0644'
path: /root/setup.sh
content: |
#! /bin/bash -x
# run your bash commands here
date > log.txt
uptime >> log.txt |
The above script creates a file setup.sh and executes it during instance creation. The output is dumped to log.txt file.
I was getting an error when launching Audacity.
The error was:
“The system has detected that another copy of Audacity is running.”
However, Audacity wasn’t running at all. Not one process. It turned out to be just a locked file located in /var/tmp/audacity-[your-username].
All you have to do is delete the entire directory and rerun Audacity.
rm -rf /var/tmp/audacity=[your-username]/ |
Once deleted, Audacity starts right up with no issues.
Here’s how to read Bash variables from another file.
Contents of config.sh
#!/bin/bash var1='thisisvariableone' var2='thisisvariabletwo' |
Call config.sh from another script.
#!/bin/bash source config.sh echo var1 echo var2 |
This is extremely helpful if you have multiple scripts using a common variable. You just to update one file instead of multiple files. All the other scripts will read and pick up the same variables from a config file. You can use this to setup your global variables.
How to split a large file.
split -b 500MB httpd.log ll -lh total 1.9G -rw-r--r-- 1 root root 954M Mar 25 12:35 httpd.log -rw-r--r-- 1 root root 477M Mar 25 12:38 xaa -rw-r--r-- 1 root root 477M Mar 25 12:38 xab |
Split with an output file.
split -b 200M httpd.log split.log ll -lh total 1.9G -rw-r--r-- 1 root root 954M Mar 25 12:35 httpd.log -rw-r--r-- 1 root root 200M Mar 25 12:52 split.logaa -rw-r--r-- 1 root root 200M Mar 25 12:52 split.logab -rw-r--r-- 1 root root 200M Mar 25 12:52 split.logac -rw-r--r-- 1 root root 200M Mar 25 12:52 split.logad -rw-r--r-- 1 root root 154M Mar 25 12:52 split.logae |
Linux has tail command. What about Windows? You can use Powershell to tail a file.
Get-Content myLog.log –Wait |
Here’s how to convert multiple files to UTF-8 format.
for file in *.csv; do iconv -f ascii -t utf-8 "$file" -o "${file%.txt}.utf8.csv" done |
You can import the Matrox Monarch HD configuration on boot up from a web page. Go to:
Command Center > Automatic Configuration. Type in URL Address starting with https. Check "Load settings on device reboot." You can either power off the device or hit reset. Holding reset for more than 5 seconds does a factory reset. On next bootup, device will have configuration contained from the remote file. |
How to load crontab from file.
crontab /path/to/file.txt |
Save crontab to a file.
crontab -l > /path/to/file.txt |
Find the biggest files in the current directory. Sort by from large to small. Display only the top 20. Display in human readable format.
find -type f -exec du -Sh {} + | sort -rh | head -n 20 |