telinit:tldr:b6bd1

The command "telinit 6" is used in Linux/Unix systems to switch to runlevel 6, which is typically the reboot runlevel. Runlevels are different operating states of a system that determine which services and processes are running. In particular, runlevel 6 represents a system reboot.

Here is what happens when the "telinit 6" command is executed:

1. The init process, which is the first process started by the Linux kernel, receives the signal to change the runlevel.
2. Init checks the current runlevel and compares it with the requested runlevel (in this case, 6).
3. If the current runlevel is already 6, no action is taken.
4. If the runlevel is different from 6, several steps are performed to move the system to runlevel 6:
   • Init sends the TERM signal to all processes, allowing them to terminate gracefully.
   • Init waits for a specified period of time for the processes to terminate.
   • If any processes do not terminate within the specified time, init sends the KILL signal to forcefully terminate them.
   • Init then executes the scripts associated with runlevel 6, which include shutting down remaining services and devices.
   • Finally, the system reboots, bringing it back up in a fresh state.

In summary, the command "telinit 6" triggers a system reboot by changing the runlevel to 6, resulting in the termination of running processes and services, followed by a reboot of the system.