networking

Networking, transfer, and connectivity

curl

Tested curl examples: GET/POST/PUT/DELETE, headers, auth, cookies, uploads, redirects, retries, and scripting.
getent

Tested getent examples: passwd, group, hosts and shadow through NSS, the exit status a script reads, and the members a group listing leaves out.
lsof

Tested lsof examples: what has a file open, which process holds a port, finding a deleted file that is still using disk space, and narrowing the output.
rsync

Tested rsync examples: the trailing-slash rule, dry runs, itemised output, --delete, exclude patterns, hard links and --link-dest snapshots.
ss

Tested ss examples: listing listening sockets, finding the process holding a port, filtering by state and address, and reading the queue columns.
ssh

Tested ssh examples: key-based auth, the config file, host key verification, port forwarding, multiplexing, and reading a failed connection.
wget

Tested wget examples: downloading, resuming, retries, authentication, recursive mirroring, and scripting with exit codes.
Copy files between two machines over SSH

Transfer a file or directory tree between two machines with scp or rsync, and resume an interrupted transfer without starting over.
Find and kill whatever is using a port

Identify the process bound to a TCP port that's refusing to let a service start, then stop it.
ss vs netstat

netstat is not installed on a Debian system and ss is. The flag translations, the filter syntax netstat cannot express, and when the old name is still fine.