Hard Skill (linux):
TCP/IP, Virtualization (Proxmox, VmWare), VPN Server, Asterisk, FreePBX, Postfix, Zimbra, Zabbix, Nagios, Squid, SQL adm, BackupPC, rsync, ...

Hard Skill (windows):
AD, File Server, Terminal, MS SQl adm, 1C adm, ...