- Understand and use essential tools
  + Access a shell prompt and issue commands with correct syntax
    > Change shells
      - # usermod -s
    > Switch virtual terminals
      - Text: Alt+F2
      - GUI: Ctrl+Alt+F2
    > alias
      - one user
        + # echo "alias pshead='ps aux | head'" >> ~/.bashrc
      - all users
        + # echo "alias pshead='ps aux | head'" >> /etc/profile.d/allusers.sh
  + Use input-output redirection (>, >>, |, 2>, etc.)
    > Standard output: ./script.sh > output.txt
    > Error output: ./script.sh 2> output.txt
    > All output: ./script.sh &> output.txt
  + Use grep and regular expressions to analyze text
    > # cat /etc/ssh/sshd_config | awk '!/^#/' | grep -v ^$
  + Access remote systems using SSH
    > Text: ssh root@server.internal
    > GUI: ssh -X root@server.internal
  + Log in and switch users in multiuser targets
    > # su - user1
  + Archive, compress, unpack, and uncompress files using tar, star, gzip, and bzip2
    > # tar --help
  + Create and edit text files
    > vi, vim
  + Create, delete, copy, and move files and directories
    > cp, mkdir, rm
  + Create hard and soft links
    > ln
  + List, set, and change standard ugo/rwx permissions
    > ls -l, chmod
  + Locate, read, and use system documentation including man, info, and files in /usr/share/doc
    > # man lvextend
    > /usr/share/doc/

- Create simple shell scripts
  + Conditionally execute code (use of: if, test, [], etc.)
    > examples: /etc/init.d/functions
  + Use Looping constructs (for, etc.) to process file, command line input
    > examples: /etc/init.d/functions
  + Process script inputs ($1, $2, etc.)
    > examples: /etc/init.d/functions
  + Processing output of shell commands within a script
    > # for i in $(seq 1 3); do touch file_$i; done
  + Processing shell command exit codes
    > # bash -x script.sh
    > # echo $?

- Operate running systems
  + Boot, reboot, and shut down a system normally
    > # shutdown = systemctl poweroff
    > # reboot = systemctl reboot
  + Boot systems into different targets manually
    > grub2
      - cli
        + add: 3
        + add: systemd.unit=multi-user.target
      - graphical
        + add: systemd.unit=graphical.target
    > shell
      - # systemctl list-units --type=target
      - # systemctl get-default
      - # systemctl set-default graphical.target
  + Interrupt the boot process in order to gain access to a system
    > grub2
      - no root password
        + add: 'rd.break'
        + # mount -o remount,rw /sysroot
        + # chroot /sysroot
        + # passwd
        + # touch /.autorelabel
        + # exit
        + # exit
  + Identify CPU/memory intensive processes and kill processes
    > # ps aux
    > # top
  + Adjust process scheduling
    > # top
      - hit 'r' key
    > -20 top priority
    >  19 low priority
    > # nice
    > # renice
  + Manage tuning profiles
    > # dnf install tuned
    > # systemctl enable --now tuned.service
    > # tuned-adm --help
  + Locate and interpret system log files and journals
    > # /var/log/{cron,maillog,messages,secure}
    > systemd-journald
      - # journalctl --boot
      - # journalctl --follow
      - # journalctl --unit=crond.service
      - # journalctl _UID=1000
  + Preserve system journals
    > # mkdir /var/log/journal
    > # chgrp systemd-journal /var/log/journal
    > # chmod 2755 /var/log/journal
    > # systemctl restart systemd-journald.service
  + Start, stop, and check the status of network services
    > # systemctl status network
    > # systemctl restart network
    > # nmcli dev status
    > # nmcli con reload
    > # nmcli con down eth0
    > # nmcli con up eth0
    > # nmtui
    > files/folders
      - /etc/sysconfig/network
  + Securely transfer files between systems
    > scp

- Configure local storage
  + List, create, delete partitions on MBR and GPT disks
    > fdisk, gdisk, partprobe, mkfs, mount, lsblk
    > mbr (32bit logical addresses up to 2TB, 15 partitions - 3 primary, 12 logical)
    > gpt (64bit logical addresses up to 8million TB, 128 partitions)
  + Create and remove physical volumes
    > pvcreate, pvremove, pvs
  + Assign physical volumes to volume groups
    > vgcreate, vgremove, vgextend, vgs
  + Create and delete logical volumes
    > lvcreate, lvremove, lvs
  + Configure systems to mount file systems at boot by universally unique ID (UUID) or label
    > blkid
    > xfs_admin
  + Add new partitions and logical volumes, and swap to a system non-destructively
    > see above
    > mkswap, swapon, swapoff

- Create and configure file systems
  + Create, mount, unmount, and use vfat, ext4, and xfs file systems
    > see above
    > /etc/fstab
  + Mount and unmount network file systems using NFS
    > server
      - server1 (192.168.122.1)
      - /etc/exports
          /nfsshare/data 192.168.122.0/24(rw,no_root_squash)
          /nfsshare/user 192.168.122.0/24(rw,no_root_squash)
      - # setsebool -P use_nfs_home_dirs on
    > client
      - /etc/fstab
        + server1:/nfsshare/data /mnt/nfs nfs defaults,sync 0 0
      - autofs
        + # dnf install autofs
        + # systemctl enable --now autofs.service
        + /net
          > /etc/auto.master
              /net -hosts
        + /home
          > examples
            - # man auto.master
            - # man 5 autofs
          > /etc/auto.master
              /home /etc/auto.home
          > /etc/auto.home
              * -rw server1:/nfsshare/user/&
          > # systemctl restart autofs
  + Extend existing logical volumes
    > vgextend, lvextend, xfs_growfs, resize2fs
  + Create and configure set-GID directories for collaboration
    > # mkdir /shared
    > # groupadd sharegroup
    > # gpasswd -M user1,user2,user3 sharegroup
    > # chown nobody:sharegroup /shared
    > # chmod 2770 /shared
  + Configure disk compression
    > # dnf install kmod-kvdo vdo
    > # vdo create --name vdo01 --dev /dev/vdd --vdoLogicalSize 10G
    > # mkfs.xfs -K /dev/mapper/vdo01
    > # mkdir /vdo01
    > # cp -a /usr/share/doc/vdo/examples/systemd/VDO.mount.example /etc/systemd/system/vdo01.mount
      - What = /dev/mapper/vdo01
      - Where = /vdo01
    > # restorecon -FRv /etc/systemd/system/
    > # systemctl enable --now vdo01.mount
    > # vdostats --human-readable
    > # df -h /vdo01
    > # vdo status --name vdo01
  + Manage layered storage
    > # dnf install stratis-cli stratisd
    > # systemctl enable --now stratisd.service
    > # stratis pool create pool01 /dev/vdc
    > # stratis pool list
    > # stratis filesystem create pool01 fs01
    > # stratis pool list
    > # blkid /stratis/pool01/fs01
    > # echo 'UUID="c51fc678-afbb-4942-bbca-56f3158e946c"  /mountdir01  xfs  defaults,x-systemd.requires=stratisd.service  0 0' >> /etc/fstab
    > # mdkir /mountdir01
    > # mount -a
    > # for i in `seq 1 5`; do touch /mountdir01/file$i; done
    > # stratis filesystem snapshot pool01 fs01 fs01-snap01
    > # stratis filesystem list
    > # rm -f /mountdir01/file{1,2}
    > # mdkir /mountdir02
    > # mount /stratis/pool01/fs01-snap01 /mountdir02
    > # ls /mountdir0*
    > reboot and verify mount
  + Diagnose and correct file permission problems
    > ls -l, chmod, chown, getfacl, setfacl, lsattr, chattr

- Deploy, configure, and maintain systems
  + Schedule tasks using at and cron
    > crontab, /etc/cron.allow, /etc/cron.deny
    > at HH:MM yyyy-mm-dd, atq, /etc/at.allow, /etc/at.deny
  + Start and stop services and configure services to start automatically at boot
    > systemctl (start, stop, enable, disable)
  + Configure systems to boot into a specific target automatically
    > # systemctl get-default
    > # systemctl list-units --type=target --all
    > # systemctl set-default multi-user.target
  + Configure time service clients
    > chronyd, /etc/chrony.conf
    > # chronyc -n sources
  + Install and update software packages from Red Hat Network, a remote repository, or from the local file system
    > # man dnf.conf
    > # yum-config-manager --add-repo=ftp://192.168.122.1/pub/inst/
    > # vim /etc/yum.repos.d/custom.repo
          [repo-custom]
          baseurl=file:///mnt/
          gpgcheck=0
    > # subscription-manager register --username=redhat_username
  + Work with package module streams
    > # dnf module list
    > # dnf module list postgresql
    > # dnf module info postgresql:12
    > # dnf module enable postgresql:12
    > # dnf install postgresql
    > # dnf distro-sync
  + Modify the system bootloader
    > modify: grubby, /etc/default/grub
    > # grub2-mkconfig -o /boot/grub2/grub.cfg

- Manage basic networking
  + Configure IPv4 and IPv6 addresses
    > nmcli, nmtui, nm-connection-editor
  + Configure hostname resolution
    > hostnamectl
    > nmcli, nmtui, nm-connection-editor
    > resolution search priority /etc/nsswitch.conf
        hosts: files dns myhostname
    > don't use /etc/resolv.conf will be overwritten by NetworkManager at boot
  + Configure network services to start automatically at boot
    > ONBOOT=yes
  + Restrict network access using firewall-cmd/firewall
    > # firewall-cmd --list-all
    > # firewall-cmd --get-services

- Manage users and groups
  + Create, delete, and modify local user accounts
    > /etc/login.defs
    > /etc/skel
  + Change passwords and adjust password aging for local user accounts
    > # chage -l
  + Create, delete, and modify local groups and group memberships
    > groupadd, gpasswd
  + Configure superuser access
    > sudo

- Manage security
  + Configure firewall settings using firewall-cmd/firewalld
    > service: firewalld
    > config: firewall-cmd, firewall-config
    > info
      - # firewall-cmd --get-services
      - # firewall-cmd --list-all
  + Create and use file access control lists
    > getfacl, setfacl
  + Configure key-based authentication for SSH
    > on client use ssh-keygen, ssh-copy-id
  + Set enforcing and permissive modes for SELinux
    > /etc/sysconfig/selinux
    > setenforce
  + List and identify SELinux file and process context
    > # ls -lZ
    > # ps -eZ
  + Restore default file contexts
    > # restorecon -Fv file1
    > # restorecon -FRv folder1/
  + Use boolean settings to modify system SELinux settings
    > # getseebool -a
    > # setsebool -P
  + Diagnose and address routine SELinux policy violations
    > # yum install setroubleshoot-server
    > # sealert -a /var/log/audit/audit.log
  
- Manage containers
  + setup
    > https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/building_running_and_managing_containers/
    > # dnf module install container-tools
  + Find and retrieve container images from a remote registry
    > registries defined in /etc/containers/registries.conf
    > # podman search postgresql-10
    > # podman search --no-trunc registry.redhat.io/rhscl/postgresql-10-rhel7
    > # podman login registry.redhat.io
    > # podman pull registry.redhat.io/rhscl/postgresql-10-rhel7
  + Inspect container images
    > local
      - # podman images
      - # podman inspect registry.redhat.io/rhscl/postgresql-10-rhel7
      - # podman tag ab2bd6c55ca1 mypostgres
      - # podman rmi -f ab2bd6c55ca1
    > remote
      - # skopeo inspect docker://registry.redhat.io/rhel8/httpd-24
  + Perform container management using commands such as podman and skopeo
    > create
      - # podman create --name mypostgres registry.redhat.io/rhscl/postgresql-10-rhel7
    > inspect
      - # podman inspect cec9aae4540f
      - # podman exec -it cec9aae4540f /bin/bash
    > save
      - # podman save --help
      - # podman load --help
    > remove
      - # podman rm 54d8d38f2285
    > skopeo
      - # skopeo --help
  + Perform basic container management such as running, starting, stopping, and listing running containers
    > list
      - # podman ps -a
    > start/stop
      - # podman start mypostgres
      - # podman stop cec9aae4540f
    > run commands
      - # podman run --rm registry.redhat.io/rhel8/httpd-24 cat /etc/os-release
      - # podman run --rm registry.redhat.io/rhel8/httpd-24 ls /root/buildinfo
      - # podman run --rm registry.redhat.io/rhel8/httpd-24 cat /root/buildinfo/Dockerfile-rhel8-httpd-24-1-120
      - # podman run -dt --name website1 -p 8080:8080/tcp registry.redhat.io/rhel8/httpd-24
        + # curl --noproxy localhost http://localhost:8080
        + # podman stop website1
    > logs
      - # podman logs website1
  + Run a service inside a container
    > # vim Dockerfile
          FROM registry.access.redhat.com/ubi8/ubi-init
          RUN yum -y install httpd; yum clean all; systemctl enable httpd;
          RUN echo "RHCSA - Run a service inside a container" > /var/www/html/index.html
          RUN mkdir /etc/systemd/system/httpd.service.d/; echo -e '[Service]\nRestart=always' > /etc/systemd/system/httpd.service.d/httpd.conf
          EXPOSE 80
    > # podman build --tag myservice .
    > # setsebool -P container_manage_cgroup true
    > # podman run -dt --name website2 -p 9090:80/tcp localhost/myservice
  + Configure a container to start automatically as a systemd service
    > root
      - # podman generate systemd --name website1 > /etc/systemd/system/container-website1.service
      - # restorecon -FRv /etc/systemd/system/
      - # systemctl daemon-reload
      - # systemctl enable --now container-website1.service
      - in example above was unable to connect to website successfully upon host reboot
        + required the following edit to service file
            [Unit]
            After=network.target network-online.target
    > non-root
      - $ podman pull registry.redhat.io/rhel8/httpd-24
      - $ mkdir .httpd
      - $ echo 'user1 website up and running' > .httpd/index.html
      - $ podman create -t --name user1-website -p 8080:8080/tcp --privileged -v /home/user1/.httpd:/var/www/html registry.redhat.io/rhel8/httpd-24
      - $ podman generate systemd --files --name user1-website
      - $ mkdir -p .config/systemd/user
      - $ mv container-user1-website.service .config/systemd/user/
      - $ restorecon -FRv .config/
      - $ systemctl --user enable --now container-user1-website.service
      - $ curl --noproxy localhost http://localhost:8080/
            user1 website up and running
  + Attach persistent storage to a container
    > get image
      - # podman pull registry.access.redhat.com/ubi8/ubi
    > default location
      - # podman volume create myvol123
      - # podman volume inspect myvol123
      - # podman create -t --name myubi1 -v myvol123:/containervolume1 registry.access.redhat.com/ubi8/ubi /bin/bash
      - # podman start -ai myubi1
      - [root@5073f5958106 /]# touch /containervolume1/testfile1
      - [root@5073f5958106 /]# ls -l /containervolume1/
          -rw-r--r--. 1 root root 0 Feb  8 05:36 testfile1
      - [root@5073f5958106 /]# exit
      - # ls -l /var/lib/containers/storage/volumes/myvol123/_data/
          -rw-r--r--. 1 root root 0 Feb  8 13:36 testfile1
    > custom location
      - # mkdir /containervols
      - # podman create -t --name myubi2 --privileged -v /containervols:/mnt registry.access.redhat.com/ubi8/ubi /bin/bash
      - # podman inspect myubi2
      - # podman start -ai myubi2
      - [root@867ddc3d374b /]# touch /mnt/testfile2
      - [root@867ddc3d374b /]# ls -l /mnt/
          -rw-r--r--. 1 root root 0 Feb  9 02:40 testfile2
      - [root@867ddc3d374b /]# exit
      - # ls -l /containervols/
          -rw-r--r--. 1 root root 0 Feb  9 10:40 testfile2