RC(8) System Manager's Manual RC(8)

rc, rc.firsttime, rc.local, rc.securelevel — command scripts for system startup

rc is the command script that is invoked by init(8) when the system starts up. It performs system housekeeping chores and starts up system daemons. Additionally, rc is intricately tied to the netstart(8) script, which runs commands and daemons pertaining to the network. rc is also used to execute any rc.d(8) scripts defined in rc.conf.local(8). The rc.securelevel, rc.firsttime, and rc.local scripts hold commands which are pertinent only to a specific site.

All of these startup scripts are controlled to some extent by variables defined in rc.conf(8), which specify which daemons and services to run.

Before init(8) starts rc, it sets the process priority, umask, and resource limits according to the “daemon” login class as described in login.conf(5). It then starts rc and attempts to execute the sequence of commands therein.

The first part of rc runs an fsck(8) with option -p to “preen” all disks of minor inconsistencies resulting from the last system shutdown and to check for serious inconsistencies caused by hardware or software failure. If this auto-check and repair succeeds, then the second part of rc is run. However, if the file /fastboot exists, fsck will not be invoked. The file is then removed so that fsck will be run on subsequent boots.

The second part of rc then asks rc.conf(8) for configuration variables, mounts filesystems, saves dmesg(8) output to the file /var/run/dmesg.boot, starts system daemons, preserves editor files, clears the scratch directory /tmp, uses savecore(8) to save any possible core image that might have been generated as a result of a system crash, and relinks kernel objects in a random order.

If at any point the boot script fails, init(8) enters single-user mode, allowing the superuser a shell on the console. On exiting this mode, init again invokes rc, but this time without performing the file system preen.

Before rc starts most system daemons, netstart(8) is executed.

rc.securelevel is executed by rc to start daemons that must be run before the security level changes. Following this, rc then sets the security level to '1' if it wasn't set already by rc.securelevel. See securelevel(7) for the effects of setting the security level.

If rc.firsttime exists, it is executed once and then deleted. Any output is mailed to root.

rc.local is executed towards the end of rc (it is not the very last as there are a few services that must be started at the very end). Normally, rc.local contains commands and daemons that are not part of the stock installation.

/etc/netstart
Command script for network startup.
/etc/rc
Command scripts for system startup.
/etc/rc.conf
System daemon configuration database.
/etc/rc.conf.local
Site specific daemon configuration database.
/etc/rc.d
Directory to hold rc.d(8) scripts.
/etc/rc.d/rc.subr
Functions used by the rc.d(8) scripts.
/etc/rc.firsttime
Commands run on the first boot after creation.
/etc/rc.local
Site specific command scripts for system startup.
/etc/rc.securelevel
Commands run before the security level changes.
/etc/rc.shutdown
Commands run at system shutdown.
/etc/examples/rc.*
Examples of site specific scripts.
/fastboot
Tells rc not to run fsck(8) during the next boot.
/var/run/dmesg.boot
Copy of dmesg(8) saved by rc at boot time.
/etc/random.seed
Random seed file read by the bootloader; updated at system startup and shutdown.
/var/db/host.random
Random seed file read by rc and the installer on upgrades; updated at system startup and shutdown.

sysctl.conf(5), securelevel(7), init(8), netstart(8), rc.conf(8), rc.d(8), rc.shutdown(8), rcctl(8)

The rc command appeared in Version 4 AT&T UNIX.

June 1, 2025 Debian