cat /etc/redhat-release
uname -a
hostnamectl
uptime

who
who -Hu
grep sh$ /etc/passwd

dmidecode -s system-manufacturer
dmidecode -s system-product-name
lshw -c system | grep product | head -1
cat /sys/class/dmi/id/product_name
cat /sys/class/dmi/id/sys_vendor

lscpu or cat /proc/cpuinfo
lsmem or cat /proc/meminfo
ifconfig -a
ethtool <devname>
lshw
lspci
dmidecode

rpm -qa
rpm -qa | grep <pkgname>
rpm -qi <pkgname>
yum repolist
yum repoinfo
yum install <pkgname>
ls -l /etc/yum.repos.d/

pstree -pa 1
ps -ef
ps auxf
systemctl

netstat -tulpn
netstat -anp
lsof -i
ss
iptables -L -n
cat /etc/resolv.conf

uname -r
cat /proc/cmdline
lsmod
modinfo <module>
sysctl -a
cat /boot/grub2/grub.cfg

dmesg
tail -f /var/log/messages
journalctl