start-stop-daemon: truncate log file for stdout.

[DentonGentry]

The initial part of that file can be useful if tailscaled is crashing or has other failures during startup. We don't want to keep the disk from hibernating by writing to it after startup.

Fixes tailscale/tailscale#7007

Signed-off-by: Denton Gentry [email protected]

[bradfitz]

Had we done this earlier, we would've never had any evidence from users about how that SIGILL bug was crashing. Or one of those earlier tun crashes.

I think we want to keep the first N bytes of the output or something, to see how it started up (tun mode, dns mode, early panics, etc). But that implies we should do it in tailscaled/Go code rather than globally here?

[bradfitz]

can you get pipe through sed '1,200p;d' in here (per tip from @creachadair) so we only print the first 200 lines and then discard the rest? then we still see start-up messages.

[DentonGentry]

Still working on this, something isn't right. No output from tailscaled is being written to the file.

dgentry@dsm7:/var$ cat  /var/packages/Tailscale/var/tailscaled.stdout.log
2023-01-19T18:18:55-08:00 Starting tailscale with: /volume1/@appstore/Tailscale/bin/tailscaled --state=/volume1/@appdata/Tailscale/tailscaled.state --socket=/volume1/@appdata/Tailscale/tailscaled.sock --port=41641 --tun=userspace-networking
dgentry@dsm7:/var$ wc -l  /var/packages/Tailscale/var/tailscaled.stdout.log
1 /var/packages/Tailscale/var/tailscaled.stdout.log
dgentry@dsm7:/var$

It is GNU sed, not busybox or something weird, and sed '1,200p;d' on a text file does print the first 200 lines.

dgentry@dsm7:/var$ /bin/sed --version
/bin/sed (GNU sed) 4.5
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.

[bradfitz]

do you need the 2>&1 first before the pipe?

[DentonGentry]

That does change the behavior, now it writes 93 lines to the file. Then it get stuck mid-line.

dgentry@dsm7:/$ cat  /var/packages/Tailscale/var/tailscaled.stdout.log
2023-01-19T19:43:58-08:00 Starting tailscale with: /volume1/@appstore/Tailscale/bin/tailscaled --state=/volume1/@appdata/Tailscale/tailscaled.state --socket=/volume1/@appdata/Tailscale/tailscaled.sock --port=41641 --tun=userspace-networking
...
wgengine: Reconfig: configuring userspace WireGuard config (with 1/29 peers)
magicsock: disco: node [jB1VP] d:f8349dfff17e6c4f now using 10.1.10.240:62625
Accept: ICMPv4{100.100.165.16:0 > 100.70.216.3:0} 84 icmp ok
Accept: TCP{100.100.165.16:49834 > 100.70.216.3:5000} 64 tcp ok
Accept: TCP{100.100.165.16:49835 > 100.70.216.3:5000} 64 tcp ok
Accept: TCP{100.100.165.16:49834 > 100.70.216.3:5000} 40 tcp non-syn
Accept: TCP{100.100.165.16:49839 > 100.70.216.3:5000} 40 tcp non-syn
Accept: TCP{100.100.165.16:49836 > 100.70.216.3:5000} 40 tcp non-syn
Accept: TCP{100.100.165.16:49834 > 100.70.216.3:5000} 52 tcp non-syn
Accept: TCP{100.100.165.16:49836dgentry@dsm7:/$

[bradfitz]

Paging @creachadair and @raggi for sed/shell help 😂

[bradfitz]

oh, I bet it's buffered and waiting to flush.

I bet that midline is on some 1K/4K boundary.

Try sed -u to turn off some buffering?

[bradfitz]

FWIW, I confirmed that both DSM6 and DSM7 have GNU sed with -u, if that's an uncommon thing (no clue)

[DentonGentry]

sed -u works much better, new log lines appear in roughly real time and the file stops growing at 201 lines — one line of the "Starting tailscale ..." echo, then 200 lines from tailscaled.

[bradfitz]

maybe we should make line 201 say it's explicitly truncated, so people don't think it's hung or something?

$ (echo one; echo two; echo three; echo four; echo five) | sed '1,3 p; 4 s,.*,[further tailscaled logs suppressed], p; d'
one
two
three
[further tailscaled logs suppressed]

[DentonGentry]

Done.