On Sat, Jun 27, 2020 at 10:33:38AM +0200, Egmont Koblinger wrote: > Hi, > > An active terminal line (/dev/pts/N), in about 6% of the cases, has a > future timestamp. > > I noticed that the command > ls -l $(tty) > occasionally prints the timestamp in "month day year" format, rather > than "month day hour:minute". This is what coreutils's "ls" does when > the timestamp is either 6+ months back in the past, or is in the > future. Let's test the "in the future" hypothesis: > > ls -l --full-time $(tty); date +%H:%M:%S.%N > occasionally produces something like > crw--w---- 1 egmont tty 136, 8 2020-06-27 09:57:28.686473296 +0200 /dev/pts/8 > 09:57:28.170717548 > Yep, the timestamp of the tty line is a slightly higher value than the > system date at a later point. > > Running > ls -l --full-time $(tty) > in an endless loop causes the seconds to increment in steps of 8, but > the subseconds part remains unchanged, like: > crw--w---- 1 egmont tty 136, 8 2020-06-27 10:07:12.686473296 +0200 /dev/pts/8 > crw--w---- 1 egmont tty 136, 8 2020-06-27 10:07:12.686473296 +0200 /dev/pts/8 > crw--w---- 1 egmont tty 136, 8 2020-06-27 10:07:20.686473296 +0200 /dev/pts/8 > crw--w---- 1 egmont tty 136, 8 2020-06-27 10:07:20.686473296 +0200 /dev/pts/8 > > drivers/tty/tty_io.c : tty_update_time() seems to be responsible for > this jump in 8 seconds, leaving the milliseconds intact. Yes, that is way on purpose, as the comment states, this is a security issue that we had to add. > I think zeroing out the milliseconds in this method would solve the > problem – although then it's maybe inconsistent that at creation time > the device would have subsecond precision which would be gone soon > afterwards. Maybe it's better to create the device with no subseconds > right away? I'll leave it to you guys to decide. What is this "problem" causing today? > I'm experiencing this on two different machines with Ubuntu 20.04, > using their 5.4.0 kernel. The method setting the seconds but not the > nanoseconds is still present in latest kernel git. Yes, this has been fixed for a while now, it should be present on all modern systems so that shows they are working properly :) thanks, greg k-h
