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

AUTHOR¶

Brendan Gregg

SEE ALSO¶

opensnoop(1)