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Servers and Linux: solutions to the most common problems

Servers and Linux systems rarely cause problems while everything is working, but then a full disk, blocked SSH access or a service that won't start turns into downtime. On this page we have gathered guides for the most common administrative problems faced by small and medium businesses, whether you run a Linux server or a Windows Server environment.

We cover everything from a full disk and file permissions, through nginx error 502 and cron jobs that don't execute, to RDP access, locked Active Directory accounts, time synchronization and certificate renewal. Each solution is explained step by step, with commands and settings you can apply immediately.

  1. Full disk on Linux server: how to free up spaceLinux server disk is full and services are not working? Learn how to find large files, clean logs, remove cache and prevent the disk from filling up again. Medium 20 min
  2. SSH connection refused: how to restore server accessSSH connection refused means the service is not listening on the port. Learn how to check sshd, the port, firewall and network and restore server access. Medium 15 min
  3. SSH permission denied publickey: how to fix server loginSSH reports permission denied publickey and won't let you into the server? Check the keys, permissions on the .ssh directory and sshd_config, then restore access without panic. Medium 20 min
  4. Linux file permissions: chmod and chown without errorsLearn how to correctly set file and folder permissions on Linux using chmod and chown commands. Avoid mistakes and ensure stable server operation. Medium 15 min
  5. Systemd service won't start: how to find the causeLearn how to diagnose why a systemd service won't start: check status, logs, configuration and dependencies. Steps for a quick fix. Medium 15 min
  6. High CPU and load on Linux: how to find the culpritLoad average is rising, CPU is at 100%, and the server is slowing down? Learn how to quickly identify the process that is overloading Linux and what to do about it. Medium 15 min
  7. Nginx 502 Bad Gateway: how to get your site back onlineSite showing 502 Bad Gateway? Find out why Nginx cannot communicate with the backend service and how to quickly get your site back online. Medium 15 min
  8. Cron job not running: how to get it startedCron job not working? Learn the most common causes and steps to get it running: check the cron service, syntax, permissions, paths, and logs. Medium 20 min
  9. Windows Server RDP cannot connect: solutionRDP cannot connect to Windows Server? Learn the most common causes and troubleshooting steps: check network, firewall, RDP service, certificates and permissions. Medium 20 min
  10. Active Directory account locked: how to unlock itAn Active Directory account got locked due to wrong password or policy. Learn how to unlock it in ADUC, via PowerShell, and how to prevent re-locking. Medium 10 min
  11. Server time synchronization: why it lags and how to fix itThe server clock is slow or jumping, and logs and certificates report errors. Check the NTP configuration, chrony and systemd-timesyncd, and restore accurate time. Medium 20 min
  12. SSL certificate renewal: how to prevent website expirationLearn how to renew an SSL certificate before it expires, prevent browser warnings, and ensure your website stays available. Steps for Let's Encrypt and commercial certificates. Medium 20 min
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