RHCSA brain dump

NOTE.md

Users:

• /etc/sudoers(.d)
• /etc/passwd
• useradd
• usermod
• userdel -r
• passwd

Groups:

• /etc/group
• groupadd
• groupmod
• groupdel
• usermod -g
• usermod -aG

Password:

• /etc/shadow
• /etc/login.defs
• chage -m 0 -M 90 -W 7 -I 14 user03
• chage -d 0 user03
• chage -l user03
• date -d "+45 days" +%F
• usermod -L user03
• usermod -L -e 2019-10-05 user03
• usermod -U
• usermod -s /sbin/nologin user03

Access control:

• chmod 644
• chown : [-R] <file/dir>
• u+s, g+s, o+t: chmod 2770 == chmod g+s
• umask:
• /etc/profile.d/local-umask.sh

SELinux:

• Apache: httpd_t, /var/www/html: httpd_sys_content_t
• getenforce && setenforce
• karg: enforcing=0 | 1, selinux= 0 | 1
• /etc/selinux/config
• Temporary: chcon -t httpd_sys_content_t <file/dir>
• Pkg: policycoreutil => restorecon, policycoretuil-python => semanage
• Permanent: semanage fcontext -a -t httpd_sys_content_t '/virtual(/.*)?' && restorecon -RFv /virtual
• apache config file: /etc/httpd/conf/httpd.conf
• SELinux booleans:
  • getsebool -a
  • getsebool httpd_enable_homedirs
  • sudo setsebool -P httpd_enable_homedirs on
  • sudo semanage boolean -l | grep httpd_enable_homedirs
  • sudo semanage boolean -l -C
  • apache: /etc/httpd/conf.d/userdir.conf
• Debug SELinux ***:
  • pkg: setroubleshoot-server
  • /var/log/audit/audit.log -> /var/log/messages
  • sealert -a /var/log/audit/audit.log
  • /var/www/html

Performance:

• kill -l
• pkill control, pkill -SIGKILL -U user, pkill -SIGKILL -t tty3
• pgrep -l -u bob
• pstree -p bob
• w
• tuned-adm active
• tuned-adm list
• tuned-adm profile throughput-performance
• tuned-adm recommend
• tuned-adm off
• nice -n 15 sha1sum, ps -o pid,comm,nice 3521, renice -n 19 3521

Packages:

• yum:

  • yum list
  • yum search KEYWORD
  • yum info PACKAGENAME
  • yum provides PATHNAME
  • yum install/update/remove
  • yum group list (hidden)
  • yum group info "RPM Development Tools"
  • yum group install "RPM Development Tools"
  • tail -5 /var/log/dnf.rpm.log
  • yum history ; yum history undo 5

• Repositories:

  • yum repolist all
  • yum-config-manager --enable rhel-8-server-debug-rpms
  • /etc/yum.repos.d/
  • yum-config-manager --add-repo="http://..."
  • rpm --import http://... && yum install http://...noarch.rpm

  ---

  [epel]
  name=xxx
  baseurl="http://.."
  enabled=1
  gpgcheck=0
  gpgkey=file:///etc/pki/rpm-gpg/..

  ---

  • yum module list perl
  • yum module info --profile module-name:stream (e.g. perl:5.24)
  • yum module install name:stream/profile, yum install @perl
  • remove and disable module stream:
    • yum module remove perl && yum module disable perl
  • switch to different stream:
    • yum module remove postgresql && yum module reset postgresql && yum module install postgresql:10

Storage:

• lsblk -fp
• add MBR / GPT: parted mklabel -> parted mkpart -> udevadm settle -> /etc/fstab
• delete MBR / GPT: parted -> print -> rm
• create FS: mkfs.vfs / mkfs.ext4
• mount FS:
  • TMP: mount / umount -> lsof
  • PER: /etc/fstab -> systemctl daemon-reload / reboot -> findmnt --verify
• create SWAP:
  • parted /dev/vdb swap1 linux-swap 1001MB 1257MB
  • udevadm settle
  • mkswap /dev/vdb2
  • swapon /dev/vdb2 -> /etc/fstab -> UUID=xxx swap swap defaults(pri=xx) 0 0
  • swapon --show
  • systemctl daemon-reload / reboot
• swapoff

Advanced Storage:

• prepare: parted mklabel -> parted mkpart -> parted set <partition#> lvm on
• create LVM: pvcreate /dev/vdb2 /dev/vdb1 -> vgcreate vg01 /dev/vdb2 /dev/vdb1 -> lvcreate -n lv01 -L 700M vg01 -> mkfs.xfs /dev/vg01/lv01 -> /etc/fstab
• remove LVM: umount /mnt/data -> lvremove /dev/vg01/lv01 -> vgremove vg01 -> pvremove /dev/vdb2 /dev/vdb1
• view LVM: pvdisplay /dev/vdb1 -> vgdisplay vg01 -> lvdisplay /dev/vg01/lv01
• extend LVM: vgextend vg01 /dev/vdb3 -> lvextend -r -L +300M /dev/vg01/lv01 -> xfs_growfs /mnt/data | resize2fs /dev/vg01/lv01
• extend LVM-SWAP: swapoff -> lvexend -L +size -> mkswap -> swapon
• reduce LVM: pvreduce vg01 /dev/vdb3 -> pvremove /dev/vdb3

NOTE: both Stratis and VDO do not require parted to initialize

Stratis (dynamic):

• yum install stratis-cli stratisd
• systemctl enable --now stratisd
• stratis pool create pool1 /dev/vdb
• stratis pool list
• stratis pool add-data pool1 /dev/vdc
• stratis pool blockdev list pool1
• stratis filesystem create pool1 filesystem1
• stratis filesystem snapshot pool1 filesystem1 snapshot1
• stratis filesystem list
• /etc/fstab -> UUID=31b9...8c55 /dir1 xfs defaults,x-systemd.requires=stratisd.service 0 0
• stratis filesystem destroy

VDO (compress and dedup):

• yum install vdo kmod-kvdo
• vdo create --name=vdo1 --device=/dev/vdd --vdoLogicalSize=50G
• vdo status --name=vdo1
• vdo list / start / stop
• /etc/fstab -> UUID=31b9...8c55 /dir1 xfs defaults,x-systemd.requires=vdo.service 0 0

NFS:

• sudo mount -o rw,sync serverb:/share mountpoint
• /etc/fstab -> serverb:/share /mountpoint nfs rw,sync 0 0
• autofs

Tar:

• tar -cf <output.tar> <input_dir>
• tar -xf <input.tar>

Netowrk:

• nnmcli

Firewall:

• firewall-cmd --set-default-zone=dmz
• firewall-cmd --permanent --zone=internal --add-source=192.168.0.0/24
• firewall-cmd --permanent --zone=internal --add-service=mysql
• firewall-cmd --reload

Hostname:

• hostnamectl -> /etc/hostname
• nmcli con mod +/-ipv4.dns -> nmcli con down -> nmcli con up -> /etc/resolve.conf
• /etc/hosts

At & Cron:

• atd && crond
• crontab -e | r | l
• ls /etc/cron*

Logs:

• rsyslog, journalctl
• /etc/rsyslog.d/*.conf -> *.debug /var/log/messages-debug
• logger -p user.debug "Debug Message Test"
• /etc/systemd/journal.conf -> set Storage=auto|persistent
• tzselect
• timedatectl list-timezones
• timedatectl set-timezone
• timedatectl set-time 9:00:00
• timedatectl set-ntp true | false
• /etc/chrony.conf -> systemctl restart chronyd -> chronyc sources -v

Services && Bootprocess:

• systemctl isolate multi-uesr.target
• systemd.unit=rescue.target
• systemd.unit=emergency.target
• reset root pw: -> rd.break -> mount -o remount,rw /sysroot -> chroot /sysroot -> passwd root -> touch /.autorelabel