Understanding SysVinit system manager
Introduction On Centos/RHEL 6 systems, the grub boot loader will load the kernel and initial RAM disk. Once the kernel has finished its startup procedure, it will hand over control to a startup manager. The SysVinit program is one such startup manager which had been used in Red Hat based systems up until RHEL 6. As of RHEL 7 onwards, the SysVinit system has been replaced in favor of systemd. In this article, we will explain the functioning of init along with run levels which describe the system state. The name SysVinit has derived from system 5 Unix and has been widely adopted in Linux as the replacement for the original BSD init. What is init? The kernel starts the init process /sbin/init with the process id 1. The init process is responsible for coordinating the start of the rest of the system services, configuring the user environment and essentially bringing the system to a functional state. Let’s take a look at the init process using the Linux top command: [sahil@linuxnix:~] $ top -p 1 -n 1 top - 14:51:28 up 210 days, 20:55, 1 user, load average: 0.00, 0.00, 0.00 Tasks: 1 total, 0 running, 1 sleeping, 0 stopped, 0 zombie Cpu(s): 1.0%us, 0.3%sy, 0.0%ni, 98.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 1921184k total, 1597396k used, 323788k free, 365232k buffers Swap: 3768316k total, 88800k used, 3679516k free, 770044k...
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