Why is my Linux server suddenly running slow?

Linux
1

Recently, my Linux server’s performance has significantly decreased. I haven’t installed any new software or updated the system. The CPU usage seems normal, but everything is still slow. I need guidance on what to check or how to troubleshoot this issue to improve performance.

2

Performance issues can really be a headache, especially when there’s no obvious culprit! Let’s dig into some potential causes and solutions:

  1. Disk Space/Usage: Sometimes, slow performance can be due to low disk space or high I/O usage. Check your disk usage with df -h and du -sh /* to make sure nothing’s eating up all your space. Also, use iotop to see if any process is heavily hitting the disk.

  2. Memory Leaks: Even if you haven’t installed new software, existing applications might be leaking memory. Use free -m to check your current memory usage and top or htop to see if some processes are consuming an unusual amount of RAM.

  3. Swap Usage: If your system is heavily swapping, it can slow things down significantly. While in free -m, check the swap usage as well. If it’s high, adding more physical RAM or optimizing your current setup might help.

  4. Network Issues: Slow network performance can sometimes present as an overall slow system. Run ifconfig or ip a to check your network interface stats and look for dropped packets or errors. Tools like ping and traceroute can help diagnose further.

  5. Hidden Services or Processes: Occasionally, rogue processes or background jobs can consume resources without showing red flags on CPU usage. ps -aux and systemctl list-units --type=service can give you more insight into what’s running. You might find some cron jobs or other scheduled tasks running at unexpected times.

  6. Temperature Check: Overheating can throttle your CPU speed even if direct CPU usage metrics look okay. You can check your system’s temperature using tools like lm-sensors (sensors command).

  7. Filesystems and Errors: File system errors can bog down performance too. Running dmesg can show you any kernel or hardware-related messages that might be relevant. If you see filesystem errors, you might need to run fsck.

  8. Log Files: Don’t forget to check /var/log/ for any unusual activity or errors being logged by your system or applications. Sometimes, constant logging due to errors can itself reduce performance.

Given you haven’t updated the system or installed new software, look into environmental factors as well. Changes in workload, new rogue scripts, or even a hardware issue could be at fault. Keep methodically checking each of these areas to pinpoint the sluggishness.

And sometimes, a simple restart can clear things up if the system’s been running for an extended period with high load. It’s a bit of a blunt tool, but sometimes effective.

Good luck, and keep us posted on what you find!

3

You could also consider the possibility of running into bottlenecks that are less visible and might have been overlooked in past performance checks:

  1. CPU Throttling: If you’re using dynamic frequency scaling (often seen with laptops and energy-saving settings), your CPU might be reducing its clock speed to save energy or due to thermal issues. Although @codecrafter mentioned temperature, you can dive deeper with cpupower frequency-info to see if your CPU is being throttled and check its current frequency states.

  2. Zombie Processes: Check for zombie processes that might be left hanging and taking up process table slots using ps -elf | grep Z. Although they don’t consume resources like regular processes, an excessive number of them indicates issues.

  3. Hardware Failures: Disk performance issues might arise due to failing hardware. Use smartctl -a /dev/sdX to display SMART data and see if the drive is reporting any critical or warning statuses. SMART (Self-Monitoring, Analysis and Reporting Technology) can often highlight potential issues before complete failure.

  4. File Descriptor Limits: Sometimes services may have reached their open file descriptor limits causing slow performance. You can check limits using ulimit -n for the shell, and per process using /proc/<pid>/limits. You might need to bump these values if they’re hitting limits.

  5. Kernel-level Issues: Kernel errors, though often reported in dmesg, might need a deeper analysis. Use tools like perf or systemtap for a more detailed look at kernel space, which can help pinpoint if it’s not user-space processes causing the delay.

  6. RAID Configuration: If you’re using RAID, degraded performance might happen due to mismatched or rebuilding arrays. Check the status of your RAID arrays with cat /proc/mdstat and ensure everything’s in optimal performance status.

  7. Filesystem Specificities: Some filesystems like Btrfs or ZFS come with their own sets of tools for diagnosing performance issues. For instance, use btrfs device stats / for Btrfs or zpool status for ZFS, to ensure the filesystem integrity isn’t compromised.

  8. Cgroup Limitations: Check if your server uses cgroups to limit resources for containers or services. Tee off the cgroup hierarchy with systemd-cgls to assess if certain cgroups have strict limits that are causing slowdowns.

  9. Interrupts and IRQ Balancing: CPU efficiency and performance can be hindered by poor balancing of interrupts. Use cat /proc/interrupts and tools like irqbalance to make sure your interrupts are being distributed effectively across all CPUs.

  10. File System Fragmentation: Though less common with Linux file systems, fragmentation can still occur, especially with non-ext file systems. Tools like e2fsck for ext file systems or filefrag can help detect and fix fragmentation issues.

Finally, if you’re running services like databases that perform numerous I/O operations, make sure their indices and caches are optimized. Running EXPLAIN within a database like MySQL or PostgreSQL can expose inefficient queries bloating performance.

Remember, performance tuning can be a pretty intricate dance that requires a bit of trial and error. It’s important to systematically tweak, verify and monitor the output/results, to avoid masking the actual issue with temporary fixes.

4

Honestly, everyone’s suggesting the usual suspects like memory leaks or disk issues, but that’s kinda the first thing anyone checks, right? Let’s get real for a second. Your server’s acting up without apparent cause? You might be dealing with subtle issues no one’s bothered to mention.

1. NUMA Issues

Linux servers can run into Non-Uniform Memory Access (NUMA) configurations problems. NUMA issues can severely degrade performance. Use the numactl command to assess and rearrange your memory allocation.

2. Kernel Resources

You need to look at kernel semaphores and other internal resources that might be exhausted. Use ipcs -s and ipcs -l. Kernel parameters might need tuning via /etc/sysctl.conf.

3. Package Updates

While you mentioned that you haven’t updated recently, keeping packages outdated can sometimes lead to performance lags due to unpatched bugs. Consider running a controlled update after checking forums for known issues with your distro’s latest versions.

4. Overscheduling

Your server could be overscheduled with crons or services under the hood that don’t emerge in top easily. Use atq and crontab -l for existing users and ensure no hidden jobs are choking your resources.

5. Container and Virtualization Overheads

Containers or VMs, though resource-efficient, can sometimes cause performance bottlenecks under certain workloads. Check docker stats or virt-manager for usage metrics. Competitors like Kubernetes can also show similar issues, but that’s on a larger scale.

6. Inotify Watches

High file system activity due to inotify watches consumes resources. Check your current limits with cat /proc/sys/fs/inotify/max_user_watches and adjust if needed.

7. Network Buffer Congestion

Network performance isn’t just about dropped packets; congestion in buffers caused by excessive traffic can slow everything down. Use ss -s and iftop to dissect whether this is the choke point.

8. User Quotas

If user-specific quotas (through quota -u) are in play, they could be imposing limits you weren’t aware of.

9. Service Misconfigurations

Look through your service configurations. Sometimes, subtle misconfigurations can kill performance. Reviewing systemctl status isn’t enough; dive into individual config files in /etc or /opt and ensure they’re optimized.

10. Misconfigured Swapiness

The way your Linux handles swapping could be all wrong. Check your swappiness setting with cat /proc/sys/vm/swappiness. Set it low (10 or 20) if you have plenty of RAM but high if you’re RAM-limited.

In a nutshell, these ‘hidden’ factors can wreak havoc. And be sure not to blindly fix one thing while ignoring others—it’s essentially trying to cut a tree with a dull axe. Good luck, and don’t get complacent with surface-level checks!