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Make Linux troubleshooting easier

Sysadmins need to ensure their Linux servers perform properly. Check out these tips for choosing the right tool for the job, preventing rootkit attacks and more.

It's up to the sysadmin to ensure that Linux servers operate at peak performance. Linux troubleshooting is of paramount concern in the data center.

Data center experts answered some of your burning Linux server troubleshooting questions around performance problems, optimization and useful tools.

How useful are the available Linux performance tools?

If you've never used pchar, pidstat or perf_events, you aren't alone. These are just a few of the underutilized Linux performance tools that characterize bandwidth, perform static and dynamic tracing, and monitor individual tasks on servers. These tools may sound obscure, but if implemented properly can significantly help Linux performance.

How do you handle malware attacks on Linux servers?

Malware problems exist on Linux servers; they just look different from the way they do on other platforms. Rootkits are most commonly the cause of such problems. They change server binaries and replace them with versions that have backdoors, which are used to compromise the security and privacy of a system. Rootkits therefore exploit your servers and make them extremely vulnerable. Use a file checker or Advanced Intrusion Detection environment to immediately identify the possible damage the rootkits caused. You should also brush up on Linux commands because some commands, such as rpm –Va, can help sysadmins with checksum verifications.

What's causing a server connection failure, and how do I fix it?

It's not always easy to detect bad transport layer security (TLS) certificates, which makes troubleshooting failed Linux server connections difficult.

First, confirm that the problem is in the certificate. Familiarize yourself with the .crt server certificate files because problems are mostly caused by unknown certificate authorities, the bodies that issue and manage security credentials and public keys for message encryption.

Certificate failure is common, but it is important to understand what else can and will go wrong, and how to fix it.

Check log files and network traffic and use the right Linux commands to troubleshoot connection failures. Commands like tcpdump check network traffic to identify which port the troubled connection uses. This command identifies which protocols have a secure or insecure port, which could be the root of a connection problem.

What do I do when my SSH server frequently disconnects?

Secure shell (SSH) connections let sysadmins manage remote Linux and Unix systems, but they also introduce the risk of being disconnected from your server, which is physically unreachable as well. This is never a good thing, but the problem grows when you're logged into numerous servers concurrently.

SSH closes idle connections to manage resources as proficiently as possible. This can inadvertently lead to sysadmin frustrations.

When you experience frequent disconnects from the server, there are two resource use settings to adjust when troubleshooting the issue: the ClientAliveInterval parameter and TCPKeepAlive. The ClientAliveInterval parameter permits the Secure Shell Daemon to sporadically check if a connection is still in use. For example, if the parameter is set at 400, the SSH server checks that the connection is still in use every 400 seconds. TCPKeepAlive confirms that the SSH sessions connection is still active. If you plan on leaving remote server log-in connections active yet idle for any period of time, extend these two intervals.

My Linux server isn't booting correctly, and my old methods for troubleshooting aren't working.

If you're accustomed to an earlier generation of Linux distributions, such as Red Hat Enterprise Linux 5, you'll find that, in the latest releases, GRUB2 and systemd change how sysadmins troubleshoot servers that don't boot correctly and require critical recovery tasks.

Several boot options have changed in Red Hat Enterprise Linux 7 and SUSE Linux Enterprise Server 12. For example, the runlevels option was eliminated from both distributions. Instead, collections of systemd services, called Systemd.units, replaced the rescue and emergency mode.

It is easier to troubleshoot a newer-version Linux server once you're familiar with how to change GRUB2 default settings. If something in the GRUB2 bootloader is preventing the server from booting correctly, sysadmins have to alter the settings in GRUB2 to fix the configuration. But the GRUB2 configuration file itself cannot be modified, they must instead rely on input files.

Next Steps

Configure Linux firewalld

Customize Linux sshd

Ask the Linux community for troubleshooting help

This was last published in September 2014

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