/dev/stderr

wikipedia:stderr

• 2>&1
• &>

• sudo -S or sudo --stdin

2>/dev/null

your-command-with-stdout-and-stderr 2>&1 | tee -a your file

Related

• CKA: Manage container stdout & stderr logs

See also

• Standard streams: /dev/stdin, /dev/stdout, /dev/stderr, /dev/null, File descriptor, set -x, 2>&1, stdbuf
• Linux logging, Cisco IOS logging