Capturing boot logs

boot-log-diff reads plain text. Any tool that writes what came over the serial console to a file works. A few things make the comparison cleaner.

What is cleaned up for you

• ANSI colour codes and carriage returns are removed.
• Blank lines are skipped.
• ISO timestamps that capture tools put in front of each line are masked, like the kernel's own [ 1.234567] timestamps.
• Bytes that are not valid UTF-8 (line noise while the board powers up) are replaced, not an error.

Linux

picocom — log to a file, quit with Ctrl-A Ctrl-X:

$ picocom -b 115200 --logfile dut.log /dev/ttyUSB0

minicom — -C captures to a file:

$ minicom -D /dev/ttyUSB0 -b 115200 -C dut.log

grabserial — made for boot logs; stops after a time or a pattern, which is what a test station needs:

$ grabserial -d /dev/ttyUSB0 -b 115200 -e 60 -q 'login:' -o dut.log

No tool at all — set the port and read it for a fixed time, straight into boot-log-diff (- reads the DUT log from stdin):

$ stty -F /dev/ttyUSB0 115200 raw -echo
$ timeout 60 cat /dev/ttyUSB0 | boot-log-diff golden.log -

Power-cycle the board after the capture has started, so the log begins with the first bootloader line, as the golden log does.

Windows

PuTTY: Session → Logging → Printable output, choose a file name, then open the serial connection. Tera Term: File → Log. Both write plain text that boot-log-diff reads directly; Windows line endings are handled.

Network consoles

Boards in a rack are often reached through a terminal server or ser2net. Read the TCP port the same way:

$ timeout 60 nc terminal-server 7001 | boot-log-diff golden.log -

Tips

• Same baud rate as the golden log. A wrong rate gives garbage that differs everywhere.
• Capture until the same point. If the golden log ends at the login prompt, stop the DUT capture there too (grabserial -q 'login:'), or every line after it is "new".
• Do not log in or type during the capture. Your typing ends up in the log.
• Long lines split in the capture file? Some terminal programs break lines at the window width. Switch line wrapping off, or use a tool that writes the raw stream (picocom, grabserial, cat).