Linux system administration, networking, security, performance tuning, scripting.
High availability, load balancers, failover, GEOIP setups.
Server storage / distributed storage: RAID, SAN, LVS, iSCSI, DRBD, GFS2, glusterfs.
Shell/bash, awk, sed, perl scripts.
PHP, Apache (including WHM/cPanel and Plesk setups), DNS, SSH, etc. - installation and configuration.
Mail (SMTP/IMAP/POP3, anti-spam, anti-virus solutions); solving mail deliverability issues.
Database tuning / troubleshooting: PostgreSQL and MySQL.
Virtualization - Xen, KVM, VMware.
Amazon AWS: EC2, S3, CloudFront.
Diskless servers / workstations, embedded devices.
I have +10 years experience with Linux administration.
I'm a contributor to Linux SCSI target framework (http://stgt.sourceforge.net/).
I helped to add Freecom FSG-3 (ARM board) support to Linux kernel.
Linux Administration (General)
Cisco Networking Concepts