Administered 40+ RHEL/CentOS and UNIX production servers — handling installation, kernel upgrades, patch management, and GRUB2 recovery — delivering 99.9% uptime and lowering unplanned downtime by 30%. Resolved 100% of L2/L3 incidents including hardware failures, OS issues, LAN/WAN outages, and remote access problems — maintaining SLA adherence with average resolution time under 4 hours. Hardened 40+ servers end-to-end — deployed firewalld zones, iptables rules, SELinux enforcing policies, ACLs, and sudo restrictions — eliminating all unauthorized access incidents over 3 years. Managed LVM storage for 30–40 servers — online volume extension, NFS, Samba, and RAID setup — resolving all disk incidents within SLA without downtime. Developed Bash scripts using awk and sed for disk alerts, log rotation, and health checks via cron — eliminating 8–10 hours of manual work per week across 40+ servers. Orchestrated 20+ KVM virtual machines using virsh and virt-manager — handled provisioning, snapshots, and live migration; implemented Cockpit for real-time server monitoring. Implemented rsync and tar backup solution for 30–40 servers — upheld 100% backup success rate with zero data loss through monthly DR drills and restore testing.