Question : My system is taking a lot of time to boot. How can I find out which services are taking long time to start? Answer : systemd-analyze command can be utilized to find out information about how much each service took to start. systemd-analyze time can provide overall information about how long it took system to start. Here is a command out which clearly shows the time taken by kernel, initrd and userspace while booting. # systemd-analyze time Startup finished in 1.267s (kernel) + … [Read more...] about CentOS / RHEL 7 : systemd-analyze command to find booting time delays
Archives for October 2016
The output of the runlevel command will indicate your previous and current runlevel separated by a single space. If there was no previous runlevel 'N' will be used as a placeholder. For example: # runlevel N 5 The output above indicates that the current runlevel is 5 and there was no previous runlevel. Changing current runlevel To change the runlevel for a system without rebooting or changing the /etc/inittab file, execute the following command as the root user: # telinit … [Read more...] about CentOS / RHEL 6 : How do I find my current runlevel?
Systemd has replaced sysVinit as the default service manager in RHEL 7. Some of the sysVinit commands have been symlinked to their RHEL 7 counterparts, however this will eventually be deprecated in favor of the standard systemd commands in the future. SysVinit V/s systemd runlevels Here is a comparison between SysVinit runlevels V/s systemd targets. Sysvinit RunlevelSystemd TargetFunction 0runlevel0.target, poweroff.targetSystem halt/shutdown 1, s, singlerunlevel1.target, … [Read more...] about CentOS / RHEL 7 : How to change runlevels (targets) with systemd
Booting into single user mode using GRUB is accomplished by editing the kernel line. single user mode can be accessed by appending an "S", "s", or "single" to the kernel command line in GRUB. This assumes that either the GRUB boot menu is not password protected or that you have access to the password if it is. Steps 1. When the system boots up, you will see the GRUB countdown, which is set to 5 seconds by default. 2. Press "Esc" to intercept this countdown and go enter a GRUB menu as … [Read more...] about CentOS / RHEL 6 : How to Boot into single user mode
Device Mapper Multipathing (or DM-multipathing) is a Linux native multipath tool, which allows you to configure multiple I/O paths between server nodes and storage arrays into a single device. The post describes the steps to un-configure and remove device mapper multipath completely from the system. Disabling the service 1. Make sure device mapper multipath is not in use. Then stop multipathd service: # service multipathd stop 2. Check multipathd service has been disable in system … [Read more...] about CentOS / RHEL 6 : How to completely remove device mapper multipath (dm-multipath)
By default root is not allowed to login through telnet for security reasons. Passwords are transmitted in plain text when you use telnet. For this reason, the root user is not allowed to connect using telnet by default. To verify root is disabled we can check the config file /etc/xinetd.d/telnet. When the parameter disable is set to yes, root user can not telnet into the system. # vi /etc/xinetd.d/telnet # default: on # description: The telnet server serves telnet sessions; it uses # … [Read more...] about CentOS / RHEL 6 : How to Disable / Enable direct root login via telnet