In CentOS/RHEL 7, the systemctl utility replaces some older power management commands used in previous versions. The table below compares the older and new equivalent systemctl commands. The old commands listed in the table still exist for compatibility reasons. Older Command systemctl equivalent Description halt systemctl haltHalts the system poweroff systemctl poweroffPowers off the system reboot systemctl rebootRestarts the system pm-suspend systemctl suspendSuspends the … [Read more...] about CentOS / RHEL 7 : Shutting Down, Suspending, or Rebooting Commands (systemctl)
Linux
CentOS / RHEL 6 : How to configure 802.1q VLAN On NIC
The configuration of the switch to support VLAN tagging is not covered in this post. You do not need to do anything for configuring native VLAN on Linux, since it only depends on switch configuration. 1. Check that the module is loaded by running the command: # lsmod | grep 8021q 2. If the module is not loaded, proceed to run the following command to load it: # modprobe 8021q 3. Proceed to configure your physical interface in /etc/sysconfig/network-scripts/ifcfg-eth#. For example, … [Read more...] about CentOS / RHEL 6 : How to configure 802.1q VLAN On NIC
RHEL 7 – RHCSA Notes – System documentation including man, info, and files in /usr/share/doc
RHEL 7 – RHCSA Notes (Cheat Sheets) Using man To find a command using a keyword : # man -k [keyword] When you know the exact command to be used, you can use the man page for that command as : # man [command] There are several sections within a man page. Most commonly used sections are listed below : Section Description 1 User Commands 4 Special files 5 system configuration files 8 system administration commands So to find configuration file … [Read more...] about RHEL 7 – RHCSA Notes – System documentation including man, info, and files in /usr/share/doc
RHEL 7 – RHCSA Notes – vi/vim editor
RHEL 7 – RHCSA Notes (Cheat Sheets) The vim editor Inserting text CommandAction iInsert text before current cursor position aAppend text after current cursor position AAppend text at the end of the current line oOpen new line below the current line OOpen new line above the current line Navigating in vi CommandAction left arrow / hmove left 1 character right arrow / lmore right 1 character up arrow / kmove up 1 line down arrow / jmove down 1 line $move to the end … [Read more...] about RHEL 7 – RHCSA Notes – vi/vim editor
RHEL 7 – RHCSA Notes (Cheat Sheets)
Red Hat Certified System Administrator better known as RHCSA exam is one of the well-known certification exam in Linux world. I've tried to write together notes that I used in my preparation of RHEL 7 RHCSA. Remember that, these are not explanatory notes, but a quick cheat sheet. The post includes links to all exam objectives for the RHCSA exam. Understand and use essential tools Access a shell prompt and issue commands with correct syntax. Use input-output redirection (>, >>, |, 2>, … [Read more...] about RHEL 7 – RHCSA Notes (Cheat Sheets)
How to add swap space in linux
Besides the RAM there is a so called Swap, which is a virtual memory, where RAM content (pages) could be swapped-in in case there is not enough RAM available anymore. This swap is located on the disc and since disc reads and writes are slower than reading from RAM, accessing memory pages there will result in a delay. In addition to filesystem creation, Linux administrators also has to pay close attention to swap usage and needs. The post describes 3 ways to add swap space to Linux systems: 1. … [Read more...] about How to add swap space in linux
CentOS / RHEL : How to collect sosreport
The "sosreport" is a tool to collect troubleshooting data on RHEL/CentOS systems. It generates a compressed tarball of debugging information that gives an overview of the most important logs and configuration of a Linux system, to be sent to Redhat Support. Among other things, the sosreport includes information about the installed rpm versions, syslog, network configuration, mounted filesystems, disk partition details, loaded kernel modules and status of all services. To run sosreport, the … [Read more...] about CentOS / RHEL : How to collect sosreport
CentOS / RHEL 7 : How to Reset root password
Resetting root password in CentOS/RHEL 7 is slightly different than the older versions. The post describes the procedure to reset the lost root password. Reboot and edit grub2 Reboot the system and press any key to stop the auto-boot from the default kernel. Press "e" after selecting the kernel line. Append rd.break to kernel When you are in edit mode, go to the line starting with linux16 and append rd.break to the end of this line. This will cause the machine to boot into … [Read more...] about CentOS / RHEL 7 : How to Reset root password
lsof : Most commonly used examples
The lsof command lists open files, sockets, and pipes. You can use lsof command to see what files are held open (such as libraries or log files) and what ports daemons listen to. You can search for open files using lsof command. lsof should be run as the superuser (root) to see all open files. When used without any arguments/options lsof lists all open files for the current active processes. # lsof COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME init … [Read more...] about lsof : Most commonly used examples
CentOS / RHEL : How to identify/match LUN presented from SAN with underlying OS disk
The post mentions few ways to exactly identify/match the LUN presented from SAN with underlying OS disk. Method 1 Execute command below command to obtain Vendor, Model and Port, Channel, SCSI-ID, LUN # cat /proc/scsi/scsi Host: scsi2 Channel: 00 Id: 00 Lun: 29 Vendor: EMC Model: SYMMETRIX Rev: 5874 Type: Direct-Access ANSI SCSI revision: 05 Host: scsi3 Channel: 00 Id: 00 Lun: 29 Vendor: EMC Model: SYMMETRIX Rev: 5874 Type: … [Read more...] about CentOS / RHEL : How to identify/match LUN presented from SAN with underlying OS disk