linux

February 9, 2025

Configure Routing on RHEL

MarvinLinux iptable, linux, os, redhat, rhel, route 0

Configure Routing Tables on RHEL

Edit the IP Table (one that will be applied permenantly even after reboot)

/etc/sysconfig/network-scripts/route- <interface name>

Apply the edited configuration file

/etc/sysconfig/network-scripts/ifup-routes <interface name>

Add dynamically (will be erased after reboot)

route add “______”

Configure DNAT on Routing Tables on RHEL

Configure with specific ports

iptables -t nat -A PREROUTING -d 105.90.15.131 -p tcp –dport 22 -j DNAT –to-destination 172.26.1.131:22

Configured without port

iptables -t nat -A PREROUTING -d 105.90.15.131 -j DNAT –to-destination 172.26.1.131

iptables -t nat -A PREROUTING -d 105.90.15.130 -j DNAT –to-destination 172.26.1.130

Deleting the DNAT with port

iptables -t nat -D PREROUTING -d 105.90.15.131 -p tcp –dport 22 -j DNAT –to-destination 172.26.1.131:22

Deleting the DNAT without port

iptables -t nat -nL OUTPUT –line-numbers

iptables -t nat -D OUTPUT {number-here}

February 9, 2025

Network Configuration on RHEL

MarvinLinux linux, network, os, redhat, rhel 0

Network Configuration on RHEL

Check which switch is connected with your adapter

tcpdump -nn -v -i bond0 -s 1500 -c 1 ‘ether[20:2]==0x2000’

*change bond0 with your interface name

Check bond which interface is on active mode

cat /sys/class/net/bond0/bonding/active_slave

Check the current status of bonding interfaces

check /proc/net/bonding/bond#

Check switch adapter status

systool -c fc_host -v |grep port_state

Network Manager CLI

To see current status

ip addr

nmcli connection show

nmcli device status

nmcli general status (current status to the connectivity)

nmcli general logging (current logging status)

nmcli device show

nmcli device show “device_name” (for one specific device)

Create new network profile

nmcli connection add type ethernet con-name “name_of_profile” ifname “interface_name_to_be_used”

Modify new network profile

nmcli connection modify “interface_name” ipv4.addresses “ip_addr/subnet” ipv4.gateway “gateway_ip_addr” ipv4.dns “dns_ip_addr” +ipv4.dns “dns_ip_addr” connection.autoconnect yes ipv4.method manual

this will create new interface_name with ip address with subnet, and gateway with 2 dns ip address, autoconnect on boot with static method

Bring network interface up

nmcli connection up “interface_name”

February 8, 2025

Firewalls on RHEL

MarvinLinux firewall, linux, os, redhat, rhel 0

Here’s firewall configuration RHEL 6 and below

Check the status for reboot persistance

chkconfig –list | grep iptables

Command to add the firewall to accept traffic with port 22 on source 192.1.1.2

iptables -I INPUT 2 -p tcp –dport 22 -s 192.1.1.2 -j ACCEPT

Default location of iptables files

/etc/sysconfig/iptables

Location of iptables configuration file

/etc/sysconfig/iptables-config

Stop & Start the iptables service

service iptables stop

service iptables start

List all the iptables

service iptables status

iptables -L

Add iptables rule

iptables -A INPUT -p tcp -s 0.0.0.0./0 -m tcp –dport 20301 -j ACCEPT

Drop iptables rule

iptables -D INPUT -p tcp -s 0.0.0.0/0 -m tcp –dport 20301 -j DROP

Save the currently running iptables to the file and system

service iptables save (It automatically overwrites it to the /etc/sysconfig/iptables)

If you edited the iptable file and want to save it use

iptables-restore < /etc/sysconfig/iptables

If you edited the iptables via commands and want to save it

service iptables save

Here’s firewall configuration RHEL 7 and above

Check status & enable/disable firewall daemon

systemctl status firewalld

systemctl enable firewalld

systemctl disable firewalld

Get current firewall rules

firewall-cmd –get-default-zone

input the result zone as below

firewall-cmd –set-default-zone=home

firewall-cmd –get-active-zones

Check firewall daemon version

firewall-cmd –version

List all interfaces under specific zone

firewall-cmd –zone=public –list-interfaces

Add/Remove interfaces under specific zone

firewall-cmd –add-interface=eth0 –zone=public

firewall-cmd –remove-interface=eth0 –zone=public

Other helpful commands

firewall-cmd –get-services

firewall-cmd –permanent –get-services

firewall-cmd –panic-on (disable incoming and outgoing packets

firewall-cmd –help

Install & Open firewall daemon on GUI

yum install firewall-config firewalld-filesystem python3-firewall -y

firewall-config

February 8, 2025

Check and maintain clustering on RHEL

MarvinLinux cluster, linux, os, redhat, rhel 0

Check & Maintain clustering on RHEL

CLUSTER COMMANDS

Check Cluster Status

Check cluster status clustat

Check cluster status every x seconds clustat -i [interval]

Check cluster status with extra detail clustat -l

Check configured nodes and their votes ccs_tool lsnode

Display cluster nodes cman_tool

Cluster Resource Group Administration

Restart Resource in place clusvcadm -R [resource name]

Relocate Resource to another member clusvcadm -r [resource name] -m [member name]

Disable Resource clusvcadm -d [resource name]

Enable Resource clusvcadm -e [resource name]

Freeze Resource clusvcadm -Z [resource name]

Unfreeze Resource clusvcadm -U [resource name]

Testing Cluster Services

Status resource in test mode rg_test test [cluster config] status service [resource-name]

Start resource in test mode rg_test test [cluster config] start service [resource-name]

Stop resource in test mode rg_test test [cluster config] stop service [resource-name]

Cluster Software

cman – Red Hat Cluster Manager

lvm2-cluster – Cluster extensions for userland logical volume management tools

rgmanager – Open Source HA Resource Group Failover for Red Hat Cluster

ricci – Remote Cluster and Storage Management System

Cluster Services

Cluster Manager (cman) Manages the following services qdiskd, fenced, dlm_controld and gfs_controld

Cluster Logical Volume Manager (clvmd)

Cluster Resource Manager (rgmanager)

Cluster Management & Configuration Daemon (ricci)

Cluster Configuration Files

Cluster configuration file /etc/cluster/cluster.conf

Cluster resource scripts /usr/share/cluster/

Cluster Log File Locations

Resource Manager Log /var/log/cluster/rgmanager.log

Fencing Log /var/log/cluster/fenced.log

Quorum Disk Log /var/log/cluster/qdiskd.log

GFS Log /var/log/cluster/gfs_controld.log

DLM Log /var/log/cluster/dlm_controld.log

Corosysnc Log /var/log/cluster/corosync.log

Start ricci on both nodes and join cluster from GUI

[Stop Cluster] [Start Cluster]

# service luci stop # service cman start

# service ricci stop # service rgmanager start

# service rgmanager stop # service ricci start

# service cman stop # service luci start

How to perform maintenance such as offline PM and Cluster failover/failback test

Procedures:

clustat

/etc/cluster/cluster.conf

stop applications and database

stops process on both hosts:

clusvcadm -d mainservicegroup

service rgmanager stop

service cman stop

service corosync stop

disable cluster from starting on reboot

chkconfig/systemctl rgmanager off/disable

chkconfig/systemctl cman off/disable

chkconfig/systemctl corosync off/disable

no database should be loaded & work on the maintenance!

clustat

df -h

yum -y update

reboot

start process on both hosts:

service cman start

service rgmanager start

enable cluster to restart upon reboot

chkconfig/systemctl rgmanager on/enable

chkconfig/systemctl cman on/enable

chkconfig/systemctl corosync on/enable

clusvcadm -e mainservicegroup <— Enable on prod first

Failover & Failback test

Relocate Resource to another member (for Physical Server)

clusvcadm -r [resource name] -m [member name]

Migrate Resource to another member (for Virtual Server)

clusvcadm -M [resource name] -m [member name]

from primaryNode:

Enable Resource

clusvcadm -r mainservicegroup -m secondaryNode

from secondaryNode:

Enable Resource

clusvcadm -r mainservicegroup -m primaryNode

February 8, 2025

Tips & Tricks on RedHat Enterprise Linux (RHEL)

MarvinLinux linux, os, redhat, rhel, tip, trick 0

Here’s a few tips & tricks on RedHat Enterprise Linux (RHEL)

add/remove SNMP settings

edit the “/etc/snmp/snmpd.conf”

service snmpd reload

edit the “/etc/hosts.allow” as needed

List process & find what process is doing

ps aux

strace

Display cluster configuration

rpm -qa | grep -i cluster

clustat

pcs status

Get system information

on DellPowerEdge:

racadm getsysinfo

racadm lclog view

on RHEL hardware detects:

dmesg

Reset login attempts for users

pam_tally2 -r (reset) -u (user) userName

Reset password expiration date

chage -I -1 -m 0 -M 99999 -E -1 userName

February 8, 2025

Check disk status using smartmontools on Linux

MarvinLinux disk, linux, os, smart, smartctl, smartmontools, status 0

There’s a smart way to check the physical disk status on the Linux OS.

By using the tool named “smartmontools” ! which as obvious as it sounds, is a tool used to monitor and control the OS storage systems.

SMART stands for the Self-Monitoring, Analysis and Reporting Technology (SMART) system

It should help sysadmin to monitor the reliability of the hard drive, and predict the drive failure ahead of actual failure to prevent any incidents!

Here’s the command to scan and print out all the devices

smartctl –scan

Here’s the command to print out all the SMART information about specified disk

*it is sdd in this example

smartctl -a /dev/sdd

Here’s the command to print out all the SMART & non-SMART information about specified disk

*it is sdd in this example

smartctl -x /dev/sdd

February 8, 2025

Extend disk space on Linux on Virtual Machine

MarvinLinux disk, extend, linux, os, vm, vmware 0

Now that you have extended the disk space from VMWare ESXi. Lets check into the OS level and extend it from the OS level.

here is an example using Linux Virtual Machine (VM)

list all the disks available on the target Linux VM so we can identify which one’s extended

lsblk

once you’ve identified the target disk, you can have system rescan the disk

*sda can be changed to your target disk name

echo 1 > /sys/class/block/sda/device/rescan

use below command to make sure the device size is changed successfully

dmesg

Run command parted and resize partition to use new free space

*note that sda can be changed to your target disk name

# parted /dev/sda

GNU Parted 3.4

Using /dev/sda

Welcome to GNU Parted! Type ‘help’ to view a list of commands.

(parted)

Use command print inside parted to list current partition table

(parted) print

Model: VMware Virtual disk (scsi)

Disk /dev/sda: 365GB

Sector size (logical/physical): 512B/512B

Partition Table: msdos

Disk Flags:

Number Start End Size Type File system Flags

1 1049kB 1075MB 1074MB primary xfs boot

2 1075MB 258GB 257GB primary lvm

Use command resizepart inside parted to resize existing partition

(parted) resizepart

Partition number? 2

End? [258GB]? 365GB

Use command print inside parted to list current partition table (note that p is short for print)

(parted) p

Model: VMware Virtual disk (scsi)

Disk /dev/sda: 365GB

Sector size (logical/physical): 512B/512B

Partition Table: msdos

Disk Flags:

Number Start End Size Type File system Flags

1 1049kB 1075MB 1074MB primary xfs boot

2 1075MB 365GB 364GB primary lvm

Use command quit inside parted to exit to bash CLI

(parted) quit

Information: You may need to update /etc/fstab.

force the kernel to re-read partition table from sda

# partprobe /dev/sda

It is optional but you can force to re-read all the partitions in the system (usefull if you particularly created a new disk/partition)

# pvscan

# partx -v -a /dev/sda

We can now see the change and increase the size of LVM PV (the disk you just resize)

# pvresize /dev/sda2

You will now see free space in VG, that you can use as you wish.

Here’s other helpful tips if you want to create new logical volume after extending disk space

# pvresize /dev/sda#

# pvscan

# lvcreate -n “nameOfVolume” -L “sizeInG” “volumeGroupName”

# lvscan

# mkfs.xfs “nameOfVolume”

# mount -t xfs “nameOfVolume” “pathToMount”

# vi /etc/fstab