Root password reset:

rd.break (as parameter in bootloader)
mount
mount -o remount,rw /sysroot/
chroot /sysroot
touch /.autorelabel

User accounts and groups:

useradd
userdel
usermod
chage
groupadd
groupdel
---
/etc/passwd
/etc/shadow
/etc/group

Access Control Lists (ACL)

getfacl myfile ... get ACL info about file

setfacl -m  ... modify ACL
setfacl -x  ... remove ACL

setfacl -x u:colleague

setfacl -m u:colleague:rx myfile
setfacl -m u:boss:rwx     myfile
setfacl -m g:admins:rx    myfile

ACL on directory inherited on newly created files
setfacl -m d:u:colleague:rx mydir

RPM packages:

rpm -q -a
rpm -q -c          ... configs
rpm -q --scripts   ... scripts related to package

Yum repos:

[myrepo]
name=myrepo
baseurl=http://myrepo.com/something
gpgcheck=0
enabled=1
---
yum clean all
yum repolist all
---
/etc/yum/repos.d/myrepo.repo

Boot and GRUB:

Linux networking:

ip addr show {myinterface}
ip link show {myinterface}
ip route
ip -6 route
getent hosts {myhostname}
host {shortname, longname}
dig {longname}

---
/etc/hosts
/etc/resolv.conf
/etc/sysconfig/network-scripts/ifcfg-{myinterface}
/etc/sysconfig/network-scripts/route-{myinterface}
/etc/sysconfig/network   ... (networking, hostname, gateway directives)

SE Linux:

getsebool -a    ... shows all SE booleans
semanage boolean -l   ...  shows persistency of SE boolean 
setsebool -P     ... sets boolean persistently
getenforce
setenforce {Enforcing|Permissive}

modes:
- enforcing mode
- permissive mode  ... good for troubleshooting
- disabled mode    ... needs reboot, use permissive mode instead, relabeling takes much time
---
/etc/sysconfig/selinux  ... change SE mode permanently
/var/log/audit/audit.log
/var/log/messages
---
ls -Z myfile
semanage fcontext -l   ... list contexts
restorecon -R -vv mydir   ... recursively restore context
(/.*)?     ...  anything that is after slash
semanage fcontext -a -t httpd_sys_content_t '/mydir(/.*)?'
sealert -l {violation code}

SE configs: