Fedora running Level and Its Virtual File System/proc

When adding new hardware to an existing Linux system, you want to know the resource configuration status of the current system. How should you view it? Very convenient. The/proc file system contains kernel information about resource allocation. Among them,/proc/interrupt,/proc/dma,/proc/ioports, including system interruption, dma, and I/O port distribution. You can run the lsusb command to check whether the device is connected to the Linux system. The command lsmod will display the status of the system to load the module. Of course, you can run cat/proc/modules to check whether the device is connected to the Linux system. If a module is not loaded at the beginning, can it be installed or removed at runtime? The answer is yes. Use the "install module" or "modprobe module" command to automatically locate and insert a module to a running kernel with the superuser permission, and remove the unused module as the "rmmod modules" command.

The running level of Linux is represented by 0-6, where 0 and 6 are transitional special levels, representing shutdown and restart respectively. When a Linux system is started, the first process executed is init, which starts all other processes. This process is responsible for guiding the system to the default running level, usually 2, 3, and 5, this depends on the Linux version and the machines used. The following table lists the meanings of Typical Running levels:

Running Level 1 (single user mode) is a basic operating environment dedicated for system maintenance. A common cause of forced entry into the single-user mode is that the system cannot automatically handle file system damages, and the administrator needs to intervene to make corrections.

You can set the default running level through ln-s/lib/systemd/system/<target name>. target/etc/systemd/system/default.tar get (this command is the method on Fedora17)

The general method is to modify the/etc/inittab file. Run the runlevel command to view the current running level of the system. To change the current running level, there are two commands available: init and telinit will send a signal to the running init process and tell it to switch to the specified running level. This Command requires the superuser permission.