Linux OS Notes - robbiehume/CS-Notes GitHub Wiki
- systemctl: using systemctl to manage systems services
- systemd:
- puppet / facter
- https://unix.stackexchange.com/questions/268766/what-exactly-happens-when-i-execute-a-file-in-my-shell
- How a Unix / Linux shell script is executed
- Common Directories Explained
- FHS (Filesystem Hierarchy Standard)
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/bin: essential user binaries (programs); important system programs and utilities-
/usr/bin: non-essential command binaries
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/sbin: similar to /bin; contains essential binaries generally intended to be run by root for sysadmin stuff-
/usr/sbin: non-essential system administration binaries
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/lib: libraries essential for binaries in /bin and /sbin -
/etc: contains system-wide configuration files -
/opt: contains subdirectories for optional software packages- Commonly used by proprietary software that doesn't obey the standard file system hierarchy
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/proc: contains special files that represent system / kernel and process information -
/tmp: used by applications to store temporary files. The files are generally deleted whenever the system is restarted -
/usr: contains apps and files used by users, as opposed to by the system- Holds things that are read-only in normal operation
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/usr/local: where locally compiled apps install to by default -
/var: contains variable files, i.e. files whose content is expected to continually change during normal operation of the system, such as logs and temporary e-mail files
- systemctl vs service command
- systemd service unit configuration
- systemd service execution environment config
- systemd unit configuration files (drop-in directory)
- using systemctl to manage systems services
- Service application actions
- Status:
sudo systemctl status <application>; Starting:sudo systemctl start <application>; Stopping:sudo systemctl stop <application>; Start on boot:sudo systemctl enable <application>// run disable to no longer start at boot; Restart:sudo systemctl restart <application> - Reload:
sudo systemctl reload <application> - Reload config w/o restarting if possible, if not then restart:
sudo systemctl reload-or-restart <application>- Some services don't support reload, so this is a good command if you're not sure if it does or doesn't
- Status:
- Can do similar commands as systemctl^ (start, stop, restart, try-restart, reload, force-reload, status)
- Syntax is
sudo service <application> <command>
- systemd essentials
- understanding systems units and unit files (more recently updated)
- systemd service unit files
- The .service file goes in
/etc/systemd/system/<service_name>.service - Enable on startup:
sudo systemctl enable <service_name> - Environment variables for service: look at sample_systemd.service
- Run script before starting:
ExecStartPre; link
Processes
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ps aux: see list of all running processes
Jobs
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jobs: see list of current jobs - Jobs have three possible states in Linux: foreground, background, and stopped Processes
- Should use copytruncate instead of (or with?) create so that the programs writing to the file don't potentially get thrown off with a file descriptor change
- https://www.digitalocean.com/community/tutorials/how-to-manage-logfiles-with-logrotate-on-ubuntu-20-04
- For a sample file look at: /misc/sample_logrotate
- The file goes in /etc/logrotate.d and need to set permissions to 644