CentOS7

Resetting root password
----------------------------------------------------
$ delete rhgb quiet
# add rd.break enforcing=0 to end of linux 16 line
$ ctrl + x
$ mount -o remount,rw /sysroot
$ chroot /sysroot
$ passwd
$ mount -o remount,ro /
$ exit
$ exit
server will now reboot, you can use the new password
$restorecon /etc/shadow
$setenforce 1
$getenforce

Configure network interfaces
----------------------------------------------------
$nmtui (network manager text user interface)

#or you can edit the files directly:
$cd /etc/sysconfig/network-scripts
$vim ifcfg-eth0

Setting a hostname and making it perm on reboot
----------------------------------------------------
$nmtui
#edit the hostname
$systemctl restart systemd-hostnamed

or
$systemctl restart NetworkManager

#check the hostname persists after reboot
$hostname

Modify default DNS
----------------------------------------------------
$nmtui
$nmcli conn down enp0s3
$nmcli conn up enp0s3

or edit the file manually

$vim /etc/sysconfig/network-scripts/ifcfg-eth0
#add gateway=ip to file
#add DNS to file
#restart connection
$systemctl restart NetworkManager

Create a repo and get materials via FTP
----------------------------------------------------
$mkdir /myrepo
$cd /myrepo
$wget ftp://addressoffiles
$tar xvf packages.tgz
#now make the repo with these files
$vim /etc/yum.repos.d/myrepo.repo
#edit the file to include:
| [myrepo]
| name=myrepo
| baseurl=file:///myrepo
| gpgcheck=0
#create the repo
$createrepo /myrepo
#check it exits and has all packages
$yum repolist
# you can now yum install the packages you added to your repo
$yum install packagename

Adding Groups and Users
----------------------------------------------------
#add 3 users, mark, gallia and jono. Mark and Gallia belong to the parents group as an additional group. Jono's login shell is not interactive.
$groupadd parents
$useradd -G parents mark
$useradd -G parents gallia
#view their groups
$id gallia
#now add jono
$useradd -s /sbin/nologin jono
#show the login shell for each user
$cat /etc/passwd

Changing Directory Permissions
----------------------------------------------------
$mkdir parents/
#change parents directory to 770 for permissions, permissions are in ugo form... user (owner) - group - others
$chmod 770 parents/
#change the group for the parents directory to parents
$chgrp parents parents/
#view the permissions for each directory
$ls -l

Managing the Kernel
----------------------------------------------------
#view kernel modules
$lsmod
#view installed kernels
$rpm -qa kernel
#view current kernel
$uname -r
#import kernel and set it as the default
$rpm -ivh kernel.rpm
#create the config file
grub2-mkconfig -o /boot/grub2/grub.cfg

#remove an old kernel
$yum remove kernel-ml-4.1.3-1.el7.elrepo.x86_64

LDAP with authconfig-gtk
----------------------------------------------------
$yum install nss-pam-ldapd
#install x window
$yum search window
$yum install xorg-x11-server-Xvfb.x86_64
#start a graphical environment
$startx
$authconfig-gtk
#LDAP Base DN: dc=tammybutow,dc=com
#LDAP Server: ldap://server.tammybutow.com
#Download cert: ftp://blah.pem
#click apply

or 

$authconfig-tui
#select use LDAP
#select use LDAP Authentication
#click next
#select use TLS
#Base DN: dc=tammybutow,dc=com
#put .pem cert file in /etc/openldap/cacerts

#checkldapusers
$su - ldapuser1
$id #this will show the user's id if they exist

#restarting LDAP
$systemctl restart nslcd

Automount a filesystem
----------------------------------------------------
$yum install nfs-utils
$vim /etc/exports
#edit the file 
|/data    -rw      *(rw,no_root_sqaush)
|
|
$systemctl start nfs
$systemctl status -l nfs #tells me what errors may have occured if any
$showmount -e localhost
$systemctl restart autofs
$vim /etc/auto.master
#edit the file
|/nfsserver    /etc/auto.nfsserver
|
|
$vim /etc/auto.nfsserver
#edit the file
|blah   -rw      localhost:/data
|
|
$cd /nfsserver
$ls -a #you will see nothing
$cd blah #you will see the mounted filesystem
$ls #you will see the files in blah which is localhost:/data


Setup a cron job
----------------------------------------------------

The user mark must create a cron job that runs daily @ 15:25 local time and executes: echo hello
$Crontab –e –u mark
#edit the file
|SHELL=/bin/bash
|HOME=/
|MAILTO=”example@digitalocean.com”
|#This is a comment
|25 15 * * * echo ‘hello’

#view what cron jobs are running
$crontab -l
$crontab -u mark -l

Configure Swap Space
----------------------------------------------------

#check if swap exists
$free -m
#identify space usage and availability
$df -h
#add swap
$fallocate -l 2GB /swapfile
$ls -lh /swapfile
$chmod 600 /swapfile
$mkswap /swapfile
$swapon /swapfile
$swapon -s

#make swap perm
$vim /etc/fstab
#edit file
|/swapfile       swap    swap    sw      0       0
|
|


Find files owned by mark and copy to a directory /opt/mark
----------------------------------------------------
$cd /opt/
$mkdir mark
find /home/mark -user mark -exec cp -f {} /opt/mark/ \; 

Find strings that match a string in a file
----------------------------------------------------
$grep ‘abc’ /etc/myfile > /tmp/myfile

Find files that match a string and copy them to a destination
----------------------------------------------------
$grep 'lib' /etc/* | xargs cp -t /tmp/lib


ACLs
----------------------------------------------------
#Copy the file /etc/fstab to /var/tmp
$cp /etc/fstab /var/tmp/
#check permissions
$getfacl /var/tmp/fstab
#set gallia to have rw access
$setfacl –m u:gallia:rw- /var/tmp/fstab
#set mark to have no acess
$setfacl –m u:mark:--- /var/tmp/fstab
#All other users have the ability to read file /var/tmp/fstab
$setfacl /etc/fstab –m o::r-- /var/tmp/fstab
#verify settings
$getfacl /var/tmp/fstab

LVM
----------------------------------------------------
$lvmdiskscan

#check what's up
$df -h
$fdisk /dev/vda1
#now using the tool
$p #partition
$n #new
$l #logical
$ #enter
$ +1GB
$ t 
$ 7 #partition number
$ l # lists types
$8e #Linux LVM
$p 
$w #write
$partprobe /dev/vda1
$cat /proc/partitions #view it now available


Resize LVM
----------------------------------------------------
#Check current size 
$lvdisplay 
$df -h
$lvs
$vgs

To make a volume bigger we need to create another physical volume
$p
$n 
$e #extended helps if you need to add more later, consumes remaining space
$ #enter
$ #enter
$n
$p
$t
$5
$8e
$w
$partprobe   


Create user with specific ID already set then add password
----------------------------------------------------
$useradd -u 1234 erin
$passwd erin
#enter a password for erin



Configure Time Services
----------------------------------------------------
$yum install -y ntp
$yum install -y chrony
$systemctl enable chronyd
$systemctl start chronyd
#config is in /etc/chrony.conf
#systemctl stop ntpd

then
#ntpdate pool.ntp.org

or 
#comment out the servers not needed
#add server.tammybutow.com iburst
$timedatectl status

then
$systemctl start ntpd