Red Hat Cheatsheet

This is a quick and dirty cheatsheet on basic commands for RHEL 6, 7 and 8.

The commands where checked with the following releases

System Information
Task RHEL6 RHEL7 RHEL8
Server release info 
cat /etc/redhat-release

lsb_release -a
cat /proc/version
 
cat /etc/redhat-release
cat /proc/version
 
cat /etc/redhat-release
cat /proc/version
Server type 
dmidecode
 
dmidecode
 
dmidecode
Hardware info 
lspci
lsusb
lshal

Note: hal = hardware abstraction layer
 
lspci
lsusb
 
lspci
lsusb
Operating system 
uname -a
 
uname -a
 
uname -a
Memory 
cat /proc/meminfo (detailed)
free -om
cat /proc/slabinfo
 
cat /proc/meminfo (detailed)
free -m
cat /proc/slabinfo
 
cat /proc/meminfo (detailed)
free -m
cat /proc/slabinfo
CPU (type, number, etc) 
cat /proc/cpuinfo
 
cat /proc/cpuinfo
 
cat /proc/cpuinfo
Disk Drives 
fdisk -l
sfdisk -l (advanced server)
parted <device> print
partprobe -s <device>

smartctl -a <device>
 
fdisk -l
sfdisk -l (advanced server)
parted <device> print
partprobe -s <device>

smartctl -a <device>
 
fdisk -l
sfdisk -l (advanced server)
parted <device> print
partprobe -s <device>

smartctl -a <device>
Kernel File and associated directories 
ls -l /boot/initrd*
ls -l /boot/vmlinuz*
 
ls -l /boot/initramfs*
ls -l /boot/vmlinuz*
 
ls -l /boot/initramfs*
ls -l /boot/vmlinuz*
Kernel 32 or 64 
uname -a
uname -m
getconf -a |grep -i 'long_bit'
cat /proc/version
 
uname -a
uname -m
getconf -a |grep -i 'long_bit'
cat /proc/version
 
uname -a
uname -m
getconf -a |grep -i 'long_bit'
cat /proc/version
Display IRQ, IO Ports and DMA 
cat /proc/interrupts
cat /proc/ioports
cat /proc/dma
 
cat /proc/interrupts
cat /proc/ioports
cat /proc/dma
 
cat /proc/interrupts
cat /proc/ioports
cat /proc/dma
Memory and Swap
Task RHEL6 RHEL7 RHEL8
Memory 
cat /proc/meminfo (detailed)
free -om
 
cat /proc/meminfo (detailed)
free -m
 
cat /proc/meminfo (detailed)
free -m
Page size 
/usr/bin/getconf -a|egrep -i 'pagesize|page_size'
 
/usr/bin/getconf -a|egrep -i 'pagesize|page_size'
 
/usr/bin/getconf -a|egrep -i 'pagesize|page_size'
Display swap 
cat /proc/swaps (detailed)
swapon -s
 
cat /proc/swaps (detailed)
swapon -s
 
cat /proc/swaps (detailed)
swapon -s
Adding swap 
device:
create partition with fdisk (type 82)
file(create 50MB swap file):
dd if=/dev/zero of=/var/swapfile bs=1024 count=50000

mkswap <device>|<file>
swapon <device>|<file>

update /etc/fstab
 
device:
create partition with fdisk (type 82)
file(create 50MB swap file):
dd if=/dev/zero of=/var/swapfile bs=1024 count=50000

mkswap <device>|<file>
swapon <device>|<file>

update /etc/fstab
 
device:
create partition with fdisk (type 82)
file(create 50MB swap file):
dd if=/dev/zero of=/var/swapfile bs=1024 count=50000

mkswap <device>|<file>
swapon <device>|<file>

update /etc/fstab
Removing swap 
swapoff <device>|<file>

Remove device or file as normal
 
swapoff <device>|<file>

Remove device or file as normal
 
swapoff <device>|<file>

Remove device or file as normal
Devices, Disks and Filesystems
Task RHEL6 RHEL7 RHEL8
Disk Drives 
fdisk -l
sfdisk -l (advanced server)
parted <device> print
partprobe <device>

udevadm info -q all -n /dev/sda1
blkid
dmsetup [ls|info]
 
fdisk -l
sfdisk -l (advanced server)
parted <device> print
partprobe <device>

blkid
dmsetup [ls|info]
 
fdisk -l
sfdisk -l (advanced server)
parted <device> print
partprobe <device>

blkid
dmsetup [ls|info]
Disk serial Number, type, etc 
hdparm -i /dev/hda
hdparm -I /dev/hda (detailed)

hdparm -Tt /dev/hda (speed test)

sdparm -i /dev/sdb

cat /proc/ide/ide0/hda/model
cat /proc/scsi/scsi
 
cat /proc/ide/ide0/hda/model
cat /proc/scsi/scsi
 
hdparm -i /dev/hda
hdparm -I /dev/hda (detailed)

hdparm -Tt /dev/hda (speed test)

cat /proc/ide/ide0/hda/model
cat /proc/scsi/scsi
Disk disk partitions 
fdisk -l
sfdisk -l (advanced server)

cat /proc/partitions (very high level)
cat /etc/fstab
 
fdisk -l
sfdisk -l (advanced server)

cat /proc/partitions (very high level)
cat /etc/fstab
 
fdisk -l
sfdisk -l (advanced server)

cat /proc/partitions (very high level)
cat /etc/fstab
List Raw Partitions 
/etc/udev/rules.d/60-raw.rules
udevinfo -d or udevadm info
raw -qa
 
/etc/udev/rules.d/60-raw.rules
raw -qa
 
/etc/udev/rules.d/60-raw.rules
raw -qa
Bad Blocks 
badblocks
 
badblocks
 
badblocks
Filesystem commands 
df -k
df -h
 
df -k
df -h
 
df -k
df -h
Filesystem (create|remove) 
mkfs -t ext3 /dev/sdb1
mke2fs -t ext4 /dev/sdb1

# all point to mke2fs
mkfs.ext2
mkfs.ext3
mkfs.ext4

cat /etc/mke2fs.conf
 
mkfs -t ext3 /dev/sdb1
mke2fs -t ext4 /dev/sdb1

# all point to mke2fs
mkfs.ext2
mkfs.ext3
mkfs.ext4

cat /etc/mke2fs.conf
 
mkfs -t ext3 /dev/sdb1
mke2fs -t ext4 /dev/sdb1

# all point to mke2fs
mkfs.ext2
mkfs.ext3
mkfs.ext4

cat /etc/mke2fs.conf
Tune filessytem 
tune2fs
tune2fs -l /dev/sda1

# change reserved blocks percentage to 1%
tune2fs -m 1 /dev/sda1
 
tune2fs
tune2fs -l /dev/sda1

# change reserved blocks percentage to 1%
tune2fs -m 1 /dev/sda1
 
tune2fs
tune2fs -l /dev/sda1

# change reserved blocks percentage to 1%
tune2fs -m 1 /dev/sda1
Force fsck 
touch /forcefsck
tune2fs -l /dev/sdb<?> |grep -i 'filesystem state'
 
touch /forcefsck
tune2fs -l /dev/sdb<?> |grep -i 'filesystem state'
 
touch /forcefsck
tune2fs -l /dev/sdb<?> |grep -i 'filesystem state'
Backup filesystem 
tar
dd
cpio
 
tar
dd
cpio
 
tar
dd
cpio
Display or set the boot device 
cat /boot/grub/grub.conf
 
cat /boot/grub2/grub.cfg
 
cat /boot/grub2/grub.cfg
Create boot device (MBR) 
grub-install <raw-device>
 
grub-install <raw-device>
grub2-install <raw-device>
 
grub2-install <raw-device>
Mount/Unmount 
mount
umount
 
mount
umount
 
mount
umount
Remount filesystem 
mount -o remount,rw /
 
mount -o remount,rw /
 
mount -o remount,rw /
Boot into maintenance mode 
Enter maintenance mode 
add below to end of kernel line

single
 
Enter maintenance mode 
add below to end of linux16 line

rd.break
 
Enter maintenance mode 
add below to end of linux line

rd.break
List device drivers 
cat /proc/devices
 
cat /proc/devices
 
cat /proc/devices
Networking
Task RHEL6 RHEL7 RHEL8
Bsic network info 
/etc/sysconfig/network
/etc/sysconfig/network-scripts
 
/etc/sysconfig/network
/etc/sysconfig/network-scripts
 
/etc/sysconfig/network
/etc/sysconfig/network-scripts
Display/Configure network interfaces RHEL Networking RHEL Networking RHEL Networking
Default router 
edit /etc/sysconfig/network
 
edit /etc/sysconfig/network
 
edit /etc/sysconfig/network
Routing table 
netstat -rn
route -n
 
netstat -rn
route -n
 
netstat -rn
route -n
Change hostname 
/etc/sysconfig/network
/etc/hosts

sysctl -a |grep hostname
 
/etc/sysconfig/network
/etc/hosts

sysctl -a |grep hostname
 
/etc/sysconfig/network
/etc/hosts

sysctl -a |grep hostname
DNS setup 
/etc/resolv.conf
 
/etc/resolv.conf
 
/etc/resolv.conf
Name service switch file 
/etc/nsswitch.conf
/etc/host.conf
/etc/resolv.conf
 
/etc/nsswitch.conf
/etc/host.conf
/etc/resolv.conf
 
/etc/nsswitch.conf
/etc/host.conf
/etc/resolv.conf
Domain Name 
/etc/sysconfig/network  (HOSTNAME option)
/etc/resolv.conf
 
/etc/sysconfig/network  (HOSTNAME option)
/etc/resolv.conf
 
/etc/sysconfig/network  (HOSTNAME option)
/etc/resolv.conf
Obtain IP address routing 
ip route get <IP address>
traceroute
 
ip route get <IP address>
traceroute
 
ip route get <IP address>
traceroute
Find Services on the network 
Boot (jumpstart) servers:
rpcinfo -b bootparam 1

NFS servers:
rpcinfo -b mountd 1

NIS servers/slaves:
rpcinfo -u <yp server> ypserv
 
Boot (jumpstart) servers:
rpcinfo -b bootparam 1

NFS servers:
rpcinfo -b mountd 1

NIS servers/slaves:
rpcinfo -u <yp server> ypserv
 
Boot (jumpstart) servers:
rpcinfo -b bootparam 1

NFS servers:
rpcinfo -b mountd 1

NIS servers/slaves:
rpcinfo -u <yp server> ypserv
Crash Dump
Task RHEL6 RHEL7 RHEL8
Check installed 
rpm -qa kexec-tools
yum install kexec-tools
/etc/kdump.conf         # dump location
 
rpm -qa kexec-tools
yum install kexec-tools
/etc/kdump.conf         # dump location
 
rpm -qa kexec-tools
yum install kexec-tools
/etc/kdump.conf         # dump location
Grub configuration 
cat /etc/default/grub
crashkernel=128M
 
cat /etc/default/grub
crashkernel=128M
Enable/Disable/Start/Stop 
service kdump start
service kdump stop
service kdump status
 
systemctl enable kdump.service
systemctl disable kdump.service
systemctl start kdump.service
systemctl stop kdump.service
 
systemctl enable kdump.service
systemctl disable kdump.service
systemctl start kdump.service
systemctl stop kdump.service
Introduction 
kdump (part of kexec rpm)

/etc/kdump.conf (select where you want the dump to go)
service kdump start
chkconfig kdump on

## to crash the system
echo "c" > /proc/sysrq-trigger

crash (used to analyse crash dumps)
 
kdump (part of kexec rpm)

/etc/kdump.conf (select where you want the dump to go)

## to crash the system
echo "c" > /proc/sysrq-trigger

sosreport
coredumpctl
eu-unstrip, eu-readelf
gdb

kdump (part of kexec rpm)

/etc/kdump.conf (select where you want the dump to go)

## to crash the system
echo "c" > /proc/sysrq-trigger

sosreport
coredumpctl
eu-unstrip, eu-readelf
gdb
Performance, Monitoring and Diagnostics
Task RHEL6 RHEL7 RHEL8
CPU 
top
sar
mpstat
w          (load average)
uptime   (load average)
ps
vmstat
procinfo
oprofile
cat /proc/cpuinfo
 
top
sar
mpstat | iostate, etc         (sysstat package)
w                             (load average)
uptime                        (load average)
ps
vmstat
procinfo
oprofile
cat /proc/cpuinfo
 
top
sar
mpstat | iostate, etc         (sysstat package)
w                             (load average)
uptime                        (load average)
ps
vmstat
procinfo
oprofile
cat /proc/cpuinfo
Memory 
free
vmstat
top
procinfo
slabtop
sar
cat /proc/meminfo
 
free
vmstat
top
procinfo
slabtop
sar
cat /proc/meminfo
 
free
vmstat
top
procinfo
slabtop
sar
cat /proc/meminfo
Network 
ethtool
mii-tool
netstat
lsof
tcpdump
ip
 
ethtool
mii-tool
netstat
lsof
tcpdump
ip
 
ethtool
mii-tool
netstat
lsof
tcpdump
ip
Disk 
sar -d
iostat
vmstat
lsof
 
sar -d
iostat
vmstat
lsof
 
sar -d
iostat
vmstat
lsof
Application 
strace -p <pid>
 
strace -p <pid>
 
strace -p <pid>
NFS 
nfsstat [-c|-s]
 
nfsstat [-c|-s]
 
nfsstat [-c|-s]
Process
Kernel Modules and Parameters
Task RHEL6 RHEL7 RHEL8
Display loaded modules 
cat /proc/modules (more detailed)
lsmod
modinfo <module>
Location:
/lib/modules/`uname -r`/kernel/drivers

Config:
/etc/modprobe.conf
/etc/modprobe.d
 
cat /proc/modules (more detailed)
lsmod
modinfo <module>
Location:
/lib/modules/`uname -r`/kernel/drivers

Config:
/etc/modprobe.d
 
cat /proc/modules (more detailed)
lsmod
modinfo <module>
Location:
/lib/modules/`uname -r`/kernel/drivers

Config:
/etc/modprobe.d
Load modules 
modprobe 
insmod
 
modprobe 
insmod
 
modprobe 
insmod
Unload modules 
modprobe 
rmmod
 
modprobe 
rmmod
 
modprobe 
rmmod
Set kernel parameters (tuning) 
/etc/sysctl.conf (edit and update then reboot)
sysctl -p <filename>
sysctl -w param=value

No reboot (dynamically):
echo "250 32000 100 28" > /proc/sys/kernel/sem
echo "536870912" > /proc/sys/kernel/shmmax
echo "4096" > /proc/sys/kernel/shmmni
echo "2097152" > /proc/sys/kernel/shmall
etc.............................................
 
/etc/sysctl.conf (edit and update then reboot)
sysctl -p <filename>
sysctl -w param=value

No reboot (dynamically):
echo "250 32000 100 28" > /proc/sys/kernel/sem
echo "536870912" > /proc/sys/kernel/shmmax
echo "4096" > /proc/sys/kernel/shmmni
echo "2097152" > /proc/sys/kernel/shmall
etc.............................................
 
/etc/sysctl.conf (edit and update then reboot)
sysctl -p <filename>
sysctl -w param=value

No reboot (dynamically):
echo "250 32000 100 28" > /proc/sys/kernel/sem
echo "536870912" > /proc/sys/kernel/shmmax
echo "4096" > /proc/sys/kernel/shmmni
echo "2097152" > /proc/sys/kernel/shmall
etc.............................................
Display kernel parameters 
sysctl -a
cat /etc/sysctl.conf

cat /proc/sys/kernel/sem
cat /proc/sys/kernel/shmmax
etc...................................
 
sysctl -a
cat /etc/sysctl.conf

cat /proc/sys/kernel/sem
cat /proc/sys/kernel/shmmax
etc...................................
 
sysctl -a
cat /etc/sysctl.conf

cat /proc/sys/kernel/sem
cat /proc/sys/kernel/shmmax
etc...................................
Interprocess communication 
ipcs -a
 
ipcs -a
 
ipcs -a
Services
Task RHEL6 RHEL7 RHEL8
Display/Start/Stop, etc services RHEL Services RHEL Services RHEL Services
Patching and Packages
Task RHEL6 RHEL7 RHEL8
Packages RHEL Packages RHEL Packages RHEL Packages
List libraries required for binary program 
ldd <file>
 
ldd <file>
 
ldd <file>
Users and Groups
Task RHEL6 RHEL7 RHEL8
Display users 
cat /etc/passwd
cat /etc/shadow
 
cat /etc/passwd
cat /etc/shadow
 
cat /etc/passwd
cat /etc/shadow
Create/Remove/Modify user 
useradd
userdel
usermod
 
useradd
userdel
usermod
 
useradd
userdel
usermod
Change user password 
passwd
 
passwd
 
passwd
Create/Remoe/Modify group 
groupadd
groupdel
groupmod
 
groupadd
groupdel
groupmod
 
groupadd
groupdel
groupmod
Password files 
/etc/passwd
/etc/shadow
 
/etc/passwd
/etc/shadow
 
/etc/passwd
/etc/shadow
Useful user commands 
id -a
whoami
who
w
finger
 
id -a
whoami
who
w
finger
 
id -a
whoami
who
w
finger
Useful group commands 
groups
 
groups
 
groups
Password policy 
/etc/login.defs
 
/etc/login.defs
 
/etc/login.defs
Password aging 
chage -l 
chage <options> <user>
 
chage -l 
chage <options> <user>
 
chage -l 
chage <options> <user>
NFS
Task RHEL6 RHEL7 RHEL8
NFS daemons 
server: rpc.mountd,nfsd
client: rpc.statd, lockd
 
server: rpc.mountd,nfsd
client: rpc.statd, lockd
 
server: rpc.mountd,nfsd
client: rpc.statd, lockd
NFS files 
/etc/exports
/var/lib/nfs/etab
/var/lib/nfs/xtab
 
/etc/exports
/var/lib/nfs/etab
/var/lib/nfs/xtab
 
/etc/exports
/var/lib/nfs/etab
/var/lib/nfs/xtab
List nfs clients that have a remote mount 
/var/lib/nfs/rmtab
 
/var/lib/nfs/rmtab
 
/var/lib/nfs/rmtab
Display NFS shares 
showmount -e localhost
 
showmount -e localhost
 
showmount -e localhost
Create NFS share 
/etc/exports (edit and add share)
/sbin/service nfs reload

## /etc/exports example
/export *(rw,fsid=0,insecure,no_root_squash,sync)
 
/etc/exports (edit and add share)
/sbin/service nfs reload

## /etc/exports example
/export *(rw,fsid=0,insecure,no_root_squash,sync)
 
/etc/exports (edit and add share)
/sbin/service nfs reload

## /etc/exports example
/export *(rw,fsid=0,insecure,no_root_squash,sync)
Uncreate NFS share 
/etc/exports (edit and remove share)
/sbin/service nfs reload
 
/etc/exports (edit and remove share)
/sbin/service nfs reload
 
/etc/exports (edit and remove share)
/sbin/service nfs reload
Start/Stop/Status/Reload NFS daemons 
/sbin/service nfs start
/sbin/service nfs stop
/sbin/service nfs status
/sbin/service nfs reload
 
/sbin/service nfs start
/sbin/service nfs stop
/sbin/service nfs status
/sbin/service nfs reload
 
/sbin/service nfs start
/sbin/service nfs stop
/sbin/service nfs status
/sbin/service nfs reload
NFS performance 
nfsstat [-c|-s]
 
nfsstat [-c|-s]
 
nfsstat [-c|-s]
NTP
Task RHEL6 RHEL7 RHEL8
NTP, Chrony RHEL Time Protocols RHEL Time Protocols RHEL Time Protocols
Log Files
Task RHEL6 RHEL7 RHEL8
Messages 
/var/log/messages
 
/var/log/messages
 
/var/log/messages
Syslog 
/var/log/syslog
 
/var/log/syslog
 
/var/log/syslog
Mail 
/var/log/mail
 
/var/log/mail
 
/var/log/mail
Cron 
/var/log/cron
 
/var/log/cron
 
/var/log/cron
Boot 
dmesg
 
dmesg
 
dmesg
Security, Firewalls and SELinux
Task RHEL6 RHEL7 RHEL8
Checking the passwd/group file 
pwck
grpck
 
pwck
grpck
 
pwck
grpck
Firewall commands RHEL Firewall RHEL Firewall RHEL Firewall
SELinux commands RHEL SELinux RHEL SELinux RHEL SELinux
Miscellaneous
Task RHEL6 RHEL7 RHEL8
Shutdown 
shutdown -h (halt)
shutdown -r (reboot)

shutdown -h (halt)
shutdown -r (reboot)

shutdown -h (halt)
shutdown -r (reboot)
Init Status see Target and RunLevels see Target and RunLevels see Target and RunLevels
Startup options 
single  - use grub to edit kernel line
emergency - use grub to edit kernel line
linux rescue - use at the boot prompt

single: runlevel1, local fs mounted, no network
emergency: root fs read-only, no init files run
rescue: use cd-rom/network, root mounted as /mnt/sysimage
 
single  - use grub to edit kernel line
emergency - use grub to edit kernel line
linux rescue - use at the boot prompt

single: runlevel1, local fs mounted, no network
emergency: root fs read-only, no init files run
rescue: use cd-rom/network, root mounted as /mnt/sysimage
 
single  - use grub to edit kernel line
emergency - use grub to edit kernel line
linux rescue - use at the boot prompt

single: runlevel1, local fs mounted, no network
emergency: root fs read-only, no init files run
rescue: use cd-rom/network, root mounted as /mnt/sysimage
Boot process 
Boot sequence

    1. BIOS
    2. POST
    3. Master Boot Record (MBR) 
        - point to the bootloader GRUB or LILO
    4. GRUB (stage 1) 
        - point to GRUB stage 1_5
    5. GRUB (stage 1_5) 
        - deals with specific filesystem types 
          look at /boot/grub/*1_5 files
    6. GRUB (stage 2) 
        – reads /etc/grub.conf and displays the 
          grub menu, it specifies the kernel and 
          the initrd files
    7. KERNEL 
        - control given to the kernel
    8. INIT 
        - reads /etc/inittab and runs 
          /etc/rc.d/rc.sysinit script
Determine the run level 
runlevel
who -r
 
runlevel
who -r
 
runlevel
who -r
Obtain default run level 
/etc/inittab
 
/etc/inittab
 
/etc/inittab
List locale 
locale -a
 
locale -a
 
locale -a
Timezone 
/etc/sysconfig/clock
/usr/share/zoneinfo/zone.tab
 
/usr/share/zoneinfo/zone.tab
 
/usr/share/zoneinfo/zone.tab
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