# Nix Services, Processes, & init System [init - Wikipedia](https://en.wikipedia.org/wiki/Init) [Daemon (computing) - Wikipedia](https://en.wikipedia.org/wiki/Daemon_(computing)) - Every process has a family history/is started by some other process (parent/child), except PID=1(systemd or init) - parent PID = PPID ## Init Process > (short for _initialization_) is the first [process](https://en.wikipedia.org/wiki/Process_(computer_science) "Process (computer science)") started during [booting](https://en.wikipedia.org/wiki/Booting "Booting") of the operating system. Init is a [daemon](https://en.wikipedia.org/wiki/Daemon_(computing) "Daemon (computing)") process that continues running until the system is shut down. It is the direct or indirect [ancestor](https://en.wikipedia.org/wiki/Parent_process "Parent process") of all other processes and automatically adopts all [orphaned processes](https://en.wikipedia.org/wiki/Orphan_process "Orphan process"). Init is started by the [kernel](https://en.wikipedia.org/wiki/Kernel_(operating_system) "Kernel (operating system)") during the [booting](https://en.wikipedia.org/wiki/Booting "Booting") process; a [kernel panic](https://en.wikipedia.org/wiki/Kernel_panic "Kernel panic") will occur if the kernel is unable to start it, or it should die for any reason. Init is typically assigned [process identifier](https://en.wikipedia.org/wiki/Process_identifier "Process identifier") 1. ## Daemons [Daemon (computing) - Wikipedia](https://en.wikipedia.org/wiki/Daemon_(computing)) - Unix Convention: daemons end in d like systemd ## [[Systemd]] ## [[init (SysV)]] ## Systemd vs init(SysV) - init(SysV) - older - Can only start processes serially, contra systemd - systemd - replaces init but there's still some controversy with it - big and complicated and does a lot of things - Can start processes in parallel - pid=1 - Raspberry Pi uses systemd ## [[Launchd]] ## [[Cron]] ## Commands - Restart service - Traditional method - service myservice restart - systemd method - systemctl restart myservice.service - [[top (command)]] - [[htop (command)]] - [[ps (command)]] - [[fg (command)]] - [[bg (command)]] - [[pgrep (command)]] - [[kill (command)]] - [[pkill (command)]] - [[caffeinate (command)]] - [[Timeout (command)]]