I’m tired of always looking up CRON scheduling, so here it is including some examples.
CRON Scheduling table:
# ┌───────────── minute (0 - 59)
# │ ┌───────────── hour (0 - 23)
# │ │ ┌───────────── day of month (1 - 31)
# │ │ │ ┌───────────── month (1 - 12)
# │ │ │ │ ┌───────────── day of week (0 - 6)
# │ │ │ │ │
# │ │ │ │ │
# │ │ │ │ │
# * * * * * command to execute
Note that the day of week (0-6) typically starts with Sunday as the first index (0), so Monday = 1, Tuesday = 2 and so on. On some systems you might be able to also use 7 as Sunday.
CRON Examples:
Note that all the cron jobs output are redirected to /tmp/log.txt. If omitted, the default is to send an email to the sysadmin email address (if configured).
ip addr show => Display network interfaces and IP address ip address add 192.168.0.1 dev eth0 => Set IP address to 192.168.0.1 ethtool eth0 => Show ethernet status eth0 mii-tool eth0 => Show ethernet status for eth0 whois <domain> => Lookup whois info for domain dig <domain> => Lookup DNS info for domain host <domain> => Lookup DNS address for domain wget fileurl => Download fileurl netstat -tupl => List all active listening ports
Hardware
dmesg => List detected hardware and boot messages cat /proc/cpuinfo => Get CPU info cat /proc/meminfo => Get memory info lshw => Display hardware configuration lsblk => Display block device info free -h => Display available memory in human readable format lspci -tv => Display PCI devices lsusb -tv => Display USB devices dmidecode => Display hardware info from BIOS hdparm -tT /dev/sda => Read speed test on disk "sda" powertop => Battery life info iotop => Disk IO info smartctl => Disk status tlp-stat => Power status and battery info
Print lines of code (amount) for all .php files in current directory
find . -name '*.php' | xargs wc -l
Log something to /var/log/syslog
logger <message>
Show all group memberships for current user
id
Get username for Apache service
ps aux | grep apache
(Relatively) secure permissions on public html folder for Apache/nginx
The goal is to set root as file owner and add the www-data as group (www-data is the group of the user running apache/nginx). Then, for every user which requires write-permission, simply add them to the www-data group.
chmod 775 gives everyone R/W/X except public because they shouldn’t have write permissions
Change www-data with whatever group belonging to the user account which is running apache/nginx.
Count files in directory
ls -lah | wc -l
Create an alias for bash commands and/or custom functions
First you need to open your bash profile config file. If preferred, you can use nano and open it with: nano ~/.bashrc
Example: Add a shorthand command for ls and tail with some extra parameters:
alias l="ls -lahS" alias t='tail -n 200 $1'
As you can see, the tail command also reads file argument given to the command.
Example: Add a custom function for searching for a string in all files in current directory:
grepfor() { grep -rnw './' -e "$1" }
When done, reload your config file by running: . ~/.bashrc
Search for string in files
grep -rnw '/path/to/dir/' -e 'stringpattern'
List only files with size above 100 MB
find . -type f -size +100M -exec ls -lh {} \;
This command scans the current dir for files above 100 MB and then executes the ls -lh command for those files. You could also say -size -10M to do the same for files below 10 MB in size.
Offline version (requires .cab installer for the .NET framework): DISM.EXE /Online /Add-Package /PackagePath:C:\Temp\microsoft-windows-netfx3-ondemand-package.cab
