pct is a command line tool to manage containers (LXC) in proxmox server.
Here are some useful commands
pct enter 100
pct enter 101
pct exec 100 yum update
pct exec 100 yum update -y
pct list
pct reboot 100
pct resize 100 rootfs 100G
pct set 101 -memory 10000
pct start 100
pct documentation available at
https://pve.proxmox.com/pve-docs/pct.1.html