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Tools for Linux Troubleshooting


A basic troubleshooting skill is just necessary for a System Administrator. One way or another thing will go south, no matter how you make sure that the system is working perfectly healthy.

Patches, updates, new security holes or vulnerabilities will definitely change the whole system and if something goes wrong, then a working system will need troubleshooting.

Even new system configuration changes that are not recorded and left forgotten and cause an adverse effect that is applied to the system will cause chaos and more time will be spent in troubleshooting, only to find out that a minor change causes the whole thing.

Here are some tools below, which could provide a basic troubleshooting to a Linux system.

A general purpose logs files, which shows messages from the system.

                tail -f /var/log/messages

/var/log/  -- directories which contains log files for the system. This directory can easily fill up the space of the whole system if not the log files are not managed properly.

/etc/rsyslog.conf – configuration to rotates log files in order to control logs so it will not grow out of space

Another trick to finding a string for the instances or occurrences in the log files is to use the command below.

                grep eth0 /var/log/*

The output may be convoluted so it would be a good idea to redirect the output to another log file, for further reading or examination.

Check system processes running on the system using ps command.

Processes can slow down the system if the program or application has some memory leak and therefore consumes a lot of memory. Of course, it’s also a good thing to know whether there are some unwanted processes running on the system.

                ps -u User_Name -forest

                ps aux

To dig more, man ps, ps  --help

Another good tool is a dmesg command.

Man dmesg  - It will show that this command will print or control the kernel ring buffer

                dmesg | less
                dmesg | grep usb
                dmesg warn

Type dmesg  --help to find out more.

Network connection, online connection, internet connection whatever the terminology it would be, the connection is quite important if you need the system to be connected to the outside world. Once the system is online or connected to the outside world, if the system is vulnerable to attack then it would just take a minute or an hour before it goes down again, or someone takes control of the system remotely.

Below are some basic tips on how to get the network system up and running if there are some issues. Some of the directories mentioned below may not be the same in otherLinux distro; commands below will work on Fedora, CentOS or Red Hat system.

                /etc/resolv.conf  --set the DNS settings on the system

                /etc/sysconfig/network-scripts/ --set IP Address on Red Hat, Fedora or CentOS system

                ls -ldR /etc/network* --for other distros to check which directories contain the
                                                        network folder

                 find /etc -name "net*" -print  -find folders and subfolders with "net" folder name    
            
                route –n  -- check the routing configuration of the system which also shows the 
                default gateway 
                if the default gateway is not configured properly system will not be able to 
               get internet  access

                ping –c 3 xx.yy.zz.aa  --sends 3 counts of ping

                traceroute –n IP.Add.Re.ss  --tracks the route packets to the destination host

                 netstat - ntlupn | grep "25"  -- shows sockets with the application using it
                                                                    shows whether the port is listening or not          

Linux display user accounts information. It’s also good to know who inside your system.  And one way to do that is to use some basic commands to display such information.

Directories that hold account information.

                /etc/passwd
                /etc/shadow
                /etc/group

Command below shows user info. Use man command to display further info of the command.

                whoami  -- man whoami
                id   -- man id
                who  -- man who
                who -q
                w – man w
                last –man last
                lastb – man lastb
                su – command to switch from ordinary account to an account with admin privileges.
                su -c command -- run a single command as root


That’s it for this time guys, hope it will help for the Linux newbies out there.

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