RHCSA: Operate running systems

  • Boot, reboot, and shut down a system normally
    reboot, poweroff, shutdown, wall
    systemctl reboot/poweroff/suspend/hibernate/hybrid-sleep/halt
    The systemctl commands are preferred.
  • Boot systems into different targets manually
    systemctl get-default, systemctl set-default multi-user.target
    systemctl rescue, systemctl emergency, systemctl isolate multi-user.target
    systemctl set-default graphical.target
  • Interrupt the boot process in order to gain access to a system
    Esc in grub, e to edit, find linux16 line, CTRL-E to get to end of line and
    Boot to rescue mode:
    append system.unit=rescue.targetBoot to change root passwd:
    remove rhgb and quiet (if there)
    append rd.break enforcing=0 to break after ramdisk, and turn off SElinux
    mount –o remount,rw /sysroot
    chroot /sysroot
    passwd… etc
    exit
    mount –o remount,ro /sysroot
    exit (continues boot process)
    restorecon /etc/shadow
    setenforce enforcing
  • Identify CPU/memory intensive processes, adjust process priority with renice, and kill processes
    top, nice –n <nnn>, renice +5, kill, kill -9
    you can only lower the priority of your processes, unless you are root which can raise them too
  • Locate and interpret system log files and journals
    /var/log/*
    journalctl
  • Access a virtual machine’s console
    virt-manager
  • Start and stop virtual machines
    virt-manager
    virsh start myVM
    virtsh shutdown myVM
    virsh reboot myVM
  • Start, stop, and check the status of network services
    systemctl start/stop/status network.service

Securely transfer files between systems
scp file user@system2:/path/newfile

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