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Linux-Troubleshooting-Scenarios

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Vinayak Salunkhe
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4 min read

Introduction:

It is important to understand the issue. There should be the right approach or a step-by-step process to be followed to troubleshoot the issues. Unix./Linux is used widely and you should be aware with the issues and correct approach to resolve it. Let’s discuss on the few of them :

Linux-Troubleshooting-Scenarios

Issue 1: Server is not reachable or unable to connect

Ping the server by Hostname and IP Address

  • Command: ping <hostname>

  • Command: ping <ip_address>

Hostname/IP Address is pingable

  • No specific command needed, as the server is reachable.

Hostname is not pingable but IP Address is pingable

  • Command: cat /etc/hosts

  • Command: cat /etc/resolv.conf

  • Command: cat /etc/nsswitch.conf

  • Command: cat /etc/sysconfig/network-scripts/ifcfg-<interface> (if applicable)

Hostname/IP Address both are not pingable

  • Check other servers on the same network.

  • Check network configuration and connectivity.

Logged into server by Virtual Console, check the uptime

  • Command: uptime

Check if the server has the IP and has UP status of Network interface

  • Command: ip a or ifconfig

  • Command: cat /etc/sysconfig/network-scripts/ifcfg-<interface> (if applicable)

  • Command: ping <gateway_ip>

  • Command: route -n

  • Command: sestatus

  • Command: iptables -L

Issue 2: Unable to connect to website or an application

  • Follow the same steps as Issue 1 for checking server reachability.

  • Command: telnet <hostname or IP> <port>

Issue 3: Unable to ssh as root or any other user

  • Follow the same steps as Issue 1 for checking server reachability.

  • Command: telnet <hostname or IP> 22

  • Command: systemctl status sshd

  • Command: journalctl -u sshd

Issue 4: Disk Space is full issue or add/extend disk space

System Performance degradation detection

  • Command: top

  • Command: df -h

Action

  • Command: du -sh <directory>

  • Command: badblocks -v /dev/sda

  • Command: iostat -x 1

New disk addition (Simple partition)

  • Command: lsblk

  • Command: fdisk /dev/sdX

  • Command: mkfs.ext4 /dev/sdX1

  • Command: mount /dev/sdX1 /mnt

  • Command: echo "/dev/sdX1 /mnt ext4 defaults 0 0" >> /etc/fstab

New disk addition (LVM Partition)

  • Command: lsblk

  • Command: fdisk /dev/sdX

  • Command: pvcreate /dev/sdX1

  • Command: vgcreate <vg_name> /dev/sdX1

  • Command: lvcreate -L <size> -n <lv_name> <vg_name>

  • Command: mkfs.ext4 /dev/<vg_name>/<lv_name>

  • Command: mount /dev/<vg_name>/<lv_name> /mnt

  • Command: echo "/dev/<vg_name>/<lv_name> /mnt ext4 defaults 0 0" >> /etc/fstab

Extend LVM partition

  • Command: lsblk

  • Command: fdisk /dev/sdX

  • Command: pvcreate /dev/sdX1

  • Command: vgextend <vg_name> /dev/sdX1

  • Command: lvextend -l +100%FREE /dev/<vg_name>/<lv_name>

  • Command: resize2fs /dev/<vg_name>/<lv_name>

Issue 5: Filesystem corrupted

  • Command: cat /var/log/messages

  • Command: dmesg

  • Command: fsck /dev/sdX1

Issue 6: fstab file missing or bad entry

  • Command: cat /var/log/messages

  • Command: blkid

  • Command: vi /etc/fstab

Issue 7: Can’t cd to the directory even if the user has sudo privileges

  • Check the directory's existence.

  • Verify the pathname, permissions, and ownership of the parent directory.

  • Ensure execute permission on the target directory.

  • Verify the existence of the target directory/file.

  • Use the complete path for the target.

  • Check permissions and ownership of the parent directory and target file.

  • Ensure read permission on the target file.

Issue 9: Running Out of Memory

  • Command: free -h

  • Command: top, htop, or ps

  • Check for OOM messages in logs and sysctl.conf for memory settings.

  • Kill or restart processes.

  • Prioritize processes using nice.

  • Add or extend swap space.

  • Add more physical RAM.

Issue 10: Add/Extend the Swap Space

  • Command: dd if=/dev/zero of=/swapfile bs=1M count=<size_in_MiB>

  • Command: chmod 600 /swapfile

  • Command: mkswap /swapfile

  • Command: swapon /swapfile

  • Command: echo "/swapfile swap swap defaults 0 0" >> /etc/fstab

Issue 11: Unable to Run Certain Commands

  • Troubleshoot based on the specific command or script.

  • Check permissions, sudo configuration, paths, installation, and library availability.

Issue 12: System Unexpectedly reboot and process restart

  • Troubleshoot based on system reboot/crash reasons.

  • Check logs, system status, and custom application logs.

  • Reach out to the vendor if necessary.

Issue 13: Unable to get IP Address

  • Check IP assignment method (DHCP or Static).

  • Verify network settings and NIC status.

  • Restart the network service.

Issue 14: Backup and Restore File Permissions in Linux

  • Command: getfacl -R <dir> > permissions.acl

  • Command: setfacl --restore=permissions.acl

Please replace <hostname>, <ip_address>, <directory>, <size>, <vg_name>, <lv_name>, and <interface> with the appropriate values for your specific configuration. These commands should help you troubleshoot and resolve the mentioned Linux issues.

LinuxLinux troubleshooting