############################ Everything below are my raw notes that I took while attending an unofficial RHCSA training session. I am posting them here in hopes they will assist others who may be preparing to take this exam. My notes are my own interpretation of the lectures, and are certainly not a replacement to classroom training either through your company, or by taking the official RHCSA classes offered through Red Hat. If you are new to the Red Hat world, I strongly suggest looking into their training courses over at Red Hat. ############################
Basic things to know on test:
– Reset root passwd via single user mode
Upstart
RHEL 6 is now using upstart (upstart.ubuntu.com). SystemV stuff is finally getting deprecated, but inittab is still there.
Quick notes about Upstart:
- Upstart allows for faster boot times, running jobs concurrently - Upstart is just used for startup/shutdown/service management. - The only place I'll notice this on test is in /etc/inittab. Specifically for modifying the runlevels within /etc/inittab. - Configuration files are in /etc/init : These tell the services how to handle events such as ctrl-alt-delete, runlevels, etc.
Runlevels:
0 : os stopped 1 : single 2 : multi-user, no NFS shares 3 : full multiuser, TUI 4 : unused 5 : full multiuser, GUI 6 : Reboot
Switch runlevels by:
telinit
(init is technically NOT the command, but works as legacy for now)
1. At bootup, kernel starts /sbin/init
2. The startup event causes /etc/init/rcS.conf to fire.
3. rcS.conf then greps out the /etc/inittab to get init level, and runs it.
4. These fires off /etc/init/rc.conf, which fires off the /etc/rc.d/rc script
5. All the startup scripts in /etc/rcX.d will get fired off accordingly.
EXAM NOTE: Nothing major is really needed for the exam on upstart. Obviously know run levels.
Init Scripts:
– To view all startup files for a run level, just look at:
ex. runlevel 5 : /etc/rc.5.d ex. runlevel 3 : /etc/rc.3.d
Notes about identifiers:
- S means to start the service - K means to kill the service - After the S or K, there is a two digit number used for ordering the execution of the scripts, ie. priority... - When entering run levels, kill scripts run first, then start scripts - All the scripts reside in /etc/init.d.. they are just symlinked to the /etc/rc.X - All these symlinks are just managed by chkconfig : When you just do: chkconfigon, it'll just default the service levels based off the defualts in the init script.
EXAM NOTE: Know how to use chkconfig
Grub
Grub is responsible for the initial kernel load at boot time.
EXAM NOTE: Probably won’t need to do much with /boot/grub/grub.conf
To get into command mode when system is booting, type:
c : command mode e : edit mode a : append mode esc : brings you back to previous menu enter : boots the machine based off your selection
To get into single user mode, add a ‘s’ or the word ‘single’ to the end of the kernel command line.
EXAM NOTE: This WILL be on test. Make sure you know how to reset lost root passwd
Lab:
1. Reboot machine into single user mode and reset root passwd 2. Review a few of the init.d scripts to get familiar 3. Review the configuration files in /etc/init.