Systems Administration and Operating Systems
Systems Administration and Operating Systems tests practical administration: identity, permissions, services, storage, patching, backup, and safe troubleshooting across Windows and Linux.
Core rules
- Use groups for permissions, not individual accounts. Grant least privilege and review privileged membership.
- Linux permissions use rwx for owner, group, and others. chmod 640 means owner read/write, group read, others none. Directory execute allows traversal.
- Windows NTFS permissions are cumulative except explicit deny. Share and NTFS permissions combine; effective access is the more restrictive.
- Services need the correct logon account, dependencies, and port availability. A failure may be permissions, disk, or dependency, not the binary.
- Backups need restore tests, retention, and offsite or immutable copies. RAID improves availability, not backup.
- Change one variable at a time; capture logs and configuration before edits.
Worked example
A Linux web service cannot read /var/www/site/index.html after a deployment. ls -l shows -rw-r----- root:root. The service runs as www-data. The file is not readable by others, and www-data is not in the root group. Fix ownership to root:www-data and mode 640, then restart only if needed. Do not use chmod 777; that grants write access to everyone and hides the ownership error.
Traps
Do not use root for routine work; use sudo with accountability. Do not assume a reboot is a fix; it may clear evidence. Do not confuse backup with archive or RAID. Do not grant Full Control to solve a read error. Do not ignore time drift, which breaks authentication and logs.