The execution level ( initialization level, launch level ) is the numbered mode of operation of the operating system , which implies the presence of certain functions in it: the higher the level number, the more functions. For the first time implemented in the init initialization subsystem in the style of System V , but is also used in other initialization subsystems. The choice of the number of levels and their content differs from system to system.
Every operating system at a certain point in time is only at one of the levels of execution. The system administrator can transfer it from one runlevel to another, for example, using the init program (for example, init 3 ). On most systems, you can check the current level with the runlevel command.
Traditional runlevels
Traditionally, there are six levels of execution, numbered from 0 to 6 (level 4 is not used), but there are ten levels - from 0 to 9, and the literature mentions level S, which is synonymous with one of the levels. Common properties of traditional levels:
- 0 - actions are taken to turn off the system.
- 1 - single user mode ( eng. Single user mode ), designed for various administrative actions to restore the system; in its meaning, it is similar to safe mode in Windows , but does not repeat it completely; at this level of execution, the system is fully configured, but not a single service is running, and only one root can work from users;
- 2 - multi-user mode without network support (sometimes used as the equivalent of level 3);
- 3 - multi-user mode with network support, normal server operation mode;
- 5 - boot in multi-user mode with graphical login;
- 6 - actions to reboot the system are performed.
Literature
- B. Ward. Chapter 6. How user space starts // Linux internal device. - St. Petersburg: Peter, 2016 .-- S. 136-173. - 384 p.