Linux RHEL7 course

Unit 

1. list all unit types: systemctl -t help

2. list all unit files path: cd /usr/lib/systemd/system

Example: ftp service --> vsftpd.service

Target

1. list all target files file: 

cd /usr/lib/systemd/system

ls *.target 

2. system target

cd /usr/lib/systemd/system

ls run*

3. list all the dependencies of graphical.target

systemctl list-dependencies graphical.target | grep target

4. list status of all target

systemctl list-units --type=target --all

5. system using target path: /etc/systemd/system

6. start system go into rescue mode

A. restart system

B. input 'e'

C. find line line start with 'linux16'

D. remove the "rhgb quiet" and input "systemd.unit=rescue.target"

E. input "x" and go into rescue mode

F. input "systemctl isolate graphical.target" and go back to graphical mode

Service

1. check all service status: systemctl --type=service

2. check specific service status: systemctl status vsftpd

3. start specific service: systemctl start vsftpd

4. automatic start specific service: systemctl enable vsftpd

5. stop specific service: systemctl stop vsftpd

6. not automatic start specific service: systemctl disable vsftpd

7. label servcie, not allow to start: systemctl mask vsftpd

8. delete label: systemctl umask vsftpd

Cgroups (control resource used by specific service)

1. Check: mount | grep cgroup

2. Change the resouce of specific service: set httpd servcie memory usage limit to 1GB

A. vim /etc/systemd/system/httpd.service

Add following context below "[Service]"

MemoryLimit=1G

B. systemctl daemon-reload

C. restart the service: systemctl restart httpd.service

D. check the service: systemctl status httpd.service

Mount File System

1. Check file system: 

A. more /etc/fstab

B. /usr/systemd/system

ls *mount

2. Make personal test folder

A. cd /etc/systemd/system

B. vim test.mount

[Unit]

Description = test mount

[Mount]

Network Manager

nmcli(command line)

nmtui(non graphical screen)

tui(graphical screen)

nmcli

check network device status: nmcli dev status

check network device properties: nmcli con show

check active network device properties: nmcli con show --active

add connection: nmcli con add con-name em1 type ethernet ifname em2 ip4 192.168.0.10/24 gw4 192.168.0.1

change dns of connection: nmcli mod em2 +ip4.dns 8.8.8.8

active the connection: nmcli con up em2

disactive the connection: nmcli dev dis em2

configuration file location: /etc/sysconfig/network-scripts

check hostname: hostnamectl status

configuration file: /etc/hostname

Change hostname: hostnamectl set-hostname <new hostname>

Software bridge

Let virtual system in KVM has connection

Create a software bridge: 

1. create master: nmcli con add type bridge con-name br0 ifname br0

2. add slaves:  

nmcli con add type bridge-slave con-name br0-port1 ifname eth0 master br0

nmcli con add type bridge-slave con-name br0-port2 ifname eth1 master br0

Check software bridge: brctl show 

Network Bonding / Teaming

bond / team: several network adaptor works as one, used for performance and redendancy

bonding: original way

teaming: efficient way

Bond

1. create master

nmcli con add type bond con-name bond0 ifname bond0 

active-backup

nmcli con mod bond0 ipv4.addresses 10.0.0.10/24

nmcli con mod bond0 ipv4.method manual

2. add slave

nmcli con add type bond-slave ifname eth0 master bond0 con-name bond0-eth0

nmcli con add type bond-slave ifname eth1 master bond0 con-name bond0-eth1

3. active bond: nmcli con up bond0

4. dis-active a slave: nmcli dev dis eth1

5. check status: cat /proc/net/bonding/bond0

Team

different work mode

1. create team interface:

nmcli con add type team con-name team0 ifname team0 config '{"runner":{"name":"balance"}}'

2. determine network configuration

nmcli con mod team0 ipv4.addresses 10.0.0.10/24

nmcli con mod team0 ipv4.method manual

3. add slave

nmcli con add type team-slave ifname eth0 master team0 con-name team0-eth0

nmcli con add type team-slave ifname eth1 master team0 con-name team0-eth1

4. active team: nmcli con up team0

5. dis-active a slave: nmcli dev dis eth1

6. check status: cat /proc/net/teaming/team0

IPv6

Add IPv6 connection: nmcli con add con-name eno2 type ethernet ifname eno2 ip6 2001:db6:0:10::d000:310/64 gw6 2001:db6:0:10::1 ip4 192.168.0.10 gw4 192.168.1.0

Change IPv6 connection: nmcli con mod eno2 ipv6.address "2001:db8:0:1::c00:10/64 2001:db8:0:1::1"

Add IPv6 DNS: nmcli con mod eno2 +ipv6.dns 2001:4860:4960::8888

Journald & Rsyslogd

Journald: systemd

rsyslogd: services 

journald command: journalctl --> database

by default journald lost at reboot

can write to rsyslogd

Journald

read journald log: journalctl 

read last 10 message: journalctl -n 10

filter error message: journalctl -p err

filter time range: 

journalctl --since today

journalctl --since "2014-06-26 16:00:00" --until "2014-06-26 16:30:00"

filter with type: journalctl -o verbose

filter with specific service: journalctl _SYSTEM_UNIT=sshd.service

filter with specific PID: journalctl _PID=1462

RHEL 7 

RHCSA (RH124 RH134)

RHCE (RH254)

RHEL 7 INSTALLATION

20GB Storage

2GB Memory

/ 10GB xfs

/boot 400MB sda1

/home 500MB xfs

swap 2048MB swap

RHEL7 network adaptor name

eno: Mainborad network adaptor

ens: PCI-E network adaptor

During installation, you can use following screen to check

Ctrl+Alt+F1: main (error message)

Ctrl+Alt+F2: shell

Ctrl+Alt+F3: log (install error)

Ctrl+Alt+F4: storage-log

Ctrl+Alt+F5: program-log

Ctrl+Alt+F6: install screen

MariaDB

Migrate from Mysql to MariaDB:

1. Copy Binary data and metadata file 

2. API, Port, Protocol all the same

3. From customer side, MariaDB and Mysql is exactly same.

Mysql MYISAM --> MariaDB Maria

Mysql Innodb --> MariaDB XtraDB

Installation

server; yum groupinstall mariadb

client: yum groupinstall mariadb-client

Start command: systemctl start mariadb

Automatic start: systemctl enable mariadb

Status command: systemctl status mariadb

Stop command: systemctl stop mariadb

Configuration

Security Enhance: mysql_secure_installation

Login: mysql -u root -p

Add firewall rule for mariadb: 

firewall-cmd --permanent --add-service=mysql

firewall-cmd --reload

Operation

Check database: show databases;

Create database: create database <database name>;

Connect database: use <database name>;

Grant privilege: 

Grant <privileges> on <database name>.<table name> to <username>@<hostname> identified by <password of user>;

flush privileges;

Backup database: mysqldump -u <username> -p <password> <database name> > <dump file>

Recover database: mysql -u <username> -p <password> < <dump file>