NAME

ttysnoop - Watch output from a tty or pts device. Uses Linux eBPF/bcc.

SYNOPSIS

ttysnoop [-h] [-C] device

DESCRIPTION

ttysnoop watches a tty or pts device, and prints the same output that is appearing on that device. It can be used to mirror the output from a shell session, or the system console.

This works by use of kernel dynamic tracing of the tty_write() function. This tool will need updating in case that kernel function changes in a future kernel version.

Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

CONFIG_BPF and bcc.

OPTIONS

-C: Don't clear the screen.
-s SIZE , --datasize SIZE: Size of the transmitting buffer (default 256).
-c COUNT, --datacount COUNT: Number of times ttysnop checks for SIZE bytes of data (default 16).
device: Either a path to a tty device (eg, /dev/tty0) or a pts number (eg, the "3" from /dev/pts/3).

EXAMPLES

Snoop output from /dev/pts/2: # ttysnoop /dev/pts/2
Snoop output from /dev/pts/2 (shortcut): # ttysnoop 2
Snoop output from the system console: # ttysnoop /dev/console
Snoop output from /dev/tty0: # ttysnoop /dev/tty0

OVERHEAD

As the rate of tty_write() is expected to be very low (<100/s), the overhead of this tool is expected to be negligible.

SOURCE

This is from bcc.

: https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

OS

Linux

STABILITY

Unstable - in development.

AUTHOR

Brendan Gregg