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

       Brendan Gregg

       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.

       Snoop output from /dev/pts/2
              # ttysnoop/dev/pts/2

       Snoop output from /dev/pts/2 (shortcut)
              # ttysnoop2

       Snoop output from the system console
              # ttysnoop/dev/console

       Snoop output from /dev/tty0
              # ttysnoop/dev/tty0

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

       -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).

       Linux

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

       CONFIG_BPF and bcc.

opensnoop(1)

USER COMMANDS                                      2016-02-08                                        ttysnoop(8)

       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.

       Unstable - in development.

ttysnoop[-h][-C]device