Daemons

• A daemon (pronounced: day-mon) is a background process that can perform tasks without user interaction
• A daemon has not controlling terminal

---

Identifying a daemon process §

• Daemons usually have a parent process ID (PPID) of 1 i.e, the parent is the init process
• Daemons aren’t attached to any terminal, thus should have no TTY

# check PPID
$ ps -eo pid,ppid,cmd | grep process-name 
2276 1 /usr/bin/some-daemon-process
 
# check TTY (? in col 2 indicates absence)
$ ps -eo pid,tty,cmd | grep process-name 
2276 ? /usr/bin/some-daemon-process

It’s a general Linux rule that the names of daemons end with the letter "d"

---

Some Linux daemons §

• udisksd
• gvfsd
• systemd
• logind

When the system boot is complete, the system initialization process starts spawning (creating) daemons through a method called forking, eliminating the need for a terminal (this is what is meant by no controlling terminal).

---

Refs §

1. https://itsfoss.com/linux-daemons/