From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Subject: bug#35550: Installer: wpa_supplicant fails to start
Date: Sun, 05 May 2019 22:26:01 +0200
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	\=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\=
	\=\?utf-8\?Q\?s\?\= message of "Fri, 03 May 2019 22:51:31 +0200")
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To: 35550@debbugs.gnu.org
Cc: sirgazil <sirgazil@zoho.com>

Ludovic Court=C3=A8s <ludo@gnu.org> skribis:

> You would expect wpa_supplicant to create its PID file atomically: write
> it under a different name, then rename(2)=E2=80=A6 but no:

Regarding this PID file atomicity issue, a few other data points: Tor,
syslogd (GNU Inetutils), sshd (OpenSSH), and dbus-daemon all do the
exact same non-atomic PID file creation as wpa_supplicant.

Libdaemon (used by Avahi) does something more fancy: it acquires an
exclusive write lock (fcntl with F_SETLKW) on the PID file right after
opening it, but since shepherd does not attempt to acquire locks on PID
file, it has no effect.

systemd and GNU=C2=A0Pies don=E2=80=99t take any precautions while reading =
PID
files.  The assumption seems to be that if the file exists, then it must
contain a valid PID.

So perhaps the problem we see with =E2=80=98wpa_supplicant=E2=80=99 is else=
where.

Ludo=E2=80=99.