Linux

• https://devhints.io/

Checks

Monitoring

# See CPU + RAM usage, system stats  and open processes
top

# Only list processes making active use of the CPU
top -i

# Only list processes making active use of the CPU, and include the entire command being instead of just the tool-name
top -ci

# Prettier version of top that can be customized
htop

# Reimagined version of top, includes network and disk usage by default
btop

Systemd

# Open journalctl starting from the beginning
journalctl -b

# Open journalctl starting from the end
journalctl -e

# Show journalctl logs for the sshd service, starting from the end
journalctl -u sshd -e

OS & Distribution

# Print OS and host information
hostnamectl

# Show OS and distribution information
cat /proc/version

# Show OS and distribution information
cat /etc/os-release

# Print distribution-specific information
lsb_release -a

Hardware & kernel

# List installed kernel modules
lsmod

# Print Kernel messages
dmesg

# Print Kernel messages with humanized timestamps
dmesg -T

# SCSI hardware information
cat /proc/scsi/scsi

# Print hardware/BIOS information
dmidecode 

# Print hardware/BIOS information of a specific type
dmidecode -t 1

# List all connected hardware
lshw

# List physical network hardware
lshw -short -class network

# List physical memory hardware
lshw -class memory

# Show PCI information
lspci

# Show verbose PCI information
lspci -v

# List all block/filesystem devices
lsblk

# List block devices and partition tables
fdisk -l

Filesystems

# List clients connected to the local filesystem
showmount

SMB/CIFS

# Samba checks
smbstatus
smbstatus -S
smbstatus -b

# Samba set debug mode
smbcontrol smbd debug 1

NFS

https://www.ibm.com/docs/en/aix/7.2?topic=troubleshooting-identifying-nfs-problems

# NFS 
nfsstat

# Detailed RPC and package information
nfsstat -o all

# Every RPC "program" is bound to a specific NFS version. Use NFS/CTDB logs in combination with the program ID to identify the failing component
rpcinfo -p

UFW

# Show summary of UFW status
ufw status

# Show verbose UFW status
ufw status verbose

# Show UFW rules numbered
ufw status numbered

CTDB

# CTDB checks in a cluster
ctdb status
ctdb ip
ctdb scriptstatus
ctdb event status
ctdb uptime
ctdb statistics

# Use the onnode command to execute a command on all cluster nodes
onnode all ctdb status

Pacemaker

# Show status of the pacemaker cluster
pcs cluster status

# Show status of the pacemaker service
pcs status

# Show configured pacemaker resources
pcs resource config

# Show a specific configured resource
pcs resource show ResourceNameHere

Services

NTP

Timedatectl

# Show the current status of timedatectl
timedatectl

# List available timezones
timedatectl list-timezones

# Set the timezone to Amsterdam
timedatectl set-timezone Europe/Amsterdam

# Show verbose sync information
timedatectl timesync-status

SNMPv3 client installation

https://kifarunix.com/quick-way-to-install-and-configure-snmp-on-ubuntu-20-04/

apt install snmpd snmp libsnmp-dev
cp /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.bak
systemctl stop snmpd
net-snmp-create-v3-user -ro -X <CRYPTO-PASSWORD> -a SHA -X <PASSWORD> -x AES <USERNAME>

# /etc/snmp/snmpd.conf
sysLocation    NL;Zuid-Holland;Rotterdam, 78 MyStreet;2nd Floor;Server Room;Rack
sysContact     Me <me@example.org>
agentaddress   192.168.0.10

systemctl start snmpd
systemctl enable snmpd

# Test
snmpwalk -v3 -a SHA -A "CRYPTO" -x AES -X "PASSWORD" -l authPriv -u "USER" localhost | head

CTDB

# Stop a ctdb cluster member
ctdb stop

# Start a stopped ctdb cluster member
ctdb continue

Firewalls

UFW

# Allow access from a specific IP to a port and add a comment that show in the status
ufw allow from 10.0.0.253 to any port 22 proto tcp comment 'Allow SSH access from XYZ location'

# Delete numbered Firewall rule 56
ufw delete 56

# Disable UFW logging (prevent syslog spam)
ufw logging off

# Set UFW logging back to the default
ufw logging low

Firewalld

#placeholder
to fill in later

SNMP access

https://unix.stackexchange.com/questions/214388/how-to-let-the-firewall-of-rhel7-the-snmp-connection-passing

vim /etc/firewalld/services/snmp.xml

<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>SNMP</short>
  <description>SNMP protocol</description>
  <port protocol="udp" port="161"/>
</service>

firewall-cmd --reload
firewall-cmd --zone=public --add-service snmp --permanent
firewall-cmd --reload

Syslog

Legacy

#/etc/rsyslog.d/70-local-to-rsyslog-server.conf
# Define the hostname to send to the syslog server
$template SendHostname, "<%pri%> %timestamp% myhost.mydomain.nl %syslogtag% %msg%\n"
$ActionForwardDefaultTemplate SendHostname

*.warning @10.77.0.1

Rainerscript

Rainerscript: https://rsyslog.readthedocs.io/en/latest/rainerscript/control_structures.html

# /etc/rsyslog.d/70-local-to-rsyslog-server.conf
# Define a template and specify a hostname to send as:
template(name="SendHostname" type="string"
string="%timestamp% myhost.mydomain.nl %syslogtag% %msg%\n"
)

# Send logs to target syslog server and port
*.warning action(type="omfwd" Target="10.0.33.10" Template="SendHostname" Port="514" Protocol="udp")

Testing

# Use the logger tool to test syslog server reception
logger -p local0.error 'Hello World!'

Ceph

# ceph osd lspools
List all available pools

# List available volumes within the openstackvolumes pool
rbd ls openstackvolumes

# List all available snapshots for object volume-asd9p12o3-90b2-1238-1209-as980d7213hs, which resides in pool ghgvolumes
rbd snap ls ghgvolumes/volume-asd9p12o3-90b2-1238-1209-as980d7213hs

# Map the volume-object to the local filesystem
rbd-nbd map ghgvolumes/volume-asd9p12o3-90b2-1238-1209-as980d7213hs

# Map the volume-object as read-only to the local filesystem
rbd-nbd map --read-only ghgvolumes/volume-asd9p12o3-90b2-1238-1209-as980d7213hs

# List currently mapped objects
rbd-nbd list-mapped

# Check what filesystem and partition the device contains
fdisk -l /dev/nbd1

# Mount the device to a local folder
mount /dev/nbd1p1 /mnt/storage

# Unmount the device from the local folder
umount /mnt/storage

# 2 methods to unmap
# Unmap the mapped object
rbd-nbd unmap /dev/nbd2

# Unmap the mapped object
rbd-nbd unmap volume-asd9p12o3-90b2-1238-1209-as980d7213hs

User management

Create user (RHEL)

# Create user with a home-folder and add him to the wheel group
useradd -m john -G wheel
 
# Set a password for the john user
passwd john

# Create the SSH folder for john
mkdir -p /home/john/.ssh

# Add a public key to john's account
echo "ssh rsa-123980idfas89132hadsckjh871234" >> /home/john/.ssh/authorized_keys

# Set proper permissions for the .ssh folder and authorized_keys
chown -R john:john /home/john/.ssh
chmod 700 /home/john/.ssh
chmod 600 /home/john/.ssh/authorized_keys

Other

Throughput test

# Test bandwidth throughput with iperf
# Listen on server-A on port 5101
iperf3 -s -p 5101

# Connect to server-A from server-B
iperf3 -c 192.168.0.1 -p 5101

# Testing disk/share throughput
# Create "testfile" of size 1710x1M in current folder
time dd if=/dev/zero of=testfile bs=1M count=1710

# Create "'testfile2" of size 5x1G in current folder
time dd if=/dev/zero of=testfile2 bs=1G count=5

# Show copy-time of "testfile" to disk or share
time cp testfile /mnt/btfrs/data/<LOCATION>/

# Methods of testing disk or share throughput
# show read-time from the mount to null
time cat /mnt/btfrs/data/<FILE> > /dev/null

# show copy-time from the mount to null
time dd if=/mnt/btfrs/data/<FILE> of=/dev/null bs=1M

# show copy-time from the mount to the current folder
time cp /mnt/btfrs/data/<FILE> .

# Copy one folder to another with rsync while showing progress
rsync -avhW --no-compress --progress <source>/ <destination>/

Create different temp folder

# Create a temporary TMP folder
mkdir -p /scratch/tmp/

# Activate temporary TMP folder
export TMPDIR=/scratch/tmp

Inodes

Every file on a filesystem has a corresponding inode file.
An inode file of a folder carries names of the files and folders that exist within itself.
The name of each filesystem-object refers to an inode file.
The inode file of a file contains a kind of metadata about the file, such as the type, Inode ID, timestamp, filename and size.