Rearrange daemonization/syslog stuff and make it more resilient.

Rename --background to -D/--daemon, to match other programs (like smbd).

You can now have --syslog even without --daemon.

Avoid using atexit(); try/finally is better.

Don't just close stderr; we'll end up eating error output from ssh!
Instead, redirect stderr to a 'logger' subprocess that will send to syslog.

Delay redirecting stderr until after we know we're daemonizing, so handy
error messages can go to stderr instead of syslog.

Make pidfile stuff more resilient: support already-existing files, files
with strict permissions, outdated files containing an already-dead pid.  Add
a --pidfile option to let you specify the pidfile path.

chdir("/") while daemonizing, so that the filesystem containing $PWD can
later be unmounted without killing the daemon.

fw.done() can't wait on the firewall subprocess on exit when daemonized; we
no longer are the parent of that process.

client.py

@@ -1,10 +1,97 @@
-import struct, socket, select, errno, re
+import struct, socket, select, errno, re, signal
 import compat.ssubprocess as ssubprocess
 import helpers, ssnet, ssh
 from ssnet import SockWrapper, Handler, Proxy, Mux, MuxWrapper
 from helpers import *
 
-import os, sys, atexit, signal, syslog
+
+_loggerp = None
+def start_syslog():
+    global _loggerp
+    _loggerp = ssubprocess.Popen(['logger',
+                                  '-p', 'daemon.info',
+                                  '-t', 'sshuttle'], stdin=ssubprocess.PIPE)
+
+
+def stderr_to_syslog():
+    sys.stdout.flush()
+    sys.stderr.flush()
+    os.dup2(_loggerp.stdin.fileno(), 1)
+    os.dup2(_loggerp.stdin.fileno(), 2)
+
+
+def got_signal(signum, frame):
+    log('exiting on signal %d\n' % signum)
+    sys.exit(1)
+
+
+_pidname = None
+def check_daemon(pidfile):
+    global _pidname
+    _pidname = os.path.abspath(pidfile)
+    try:
+        oldpid = open(_pidname).read(1024)
+    except IOError, e:
+        if e.errno == errno.ENOENT:
+            return  # no pidfile, ok
+        else:
+            raise Fatal("can't read %s: %s" % (_pidname, e))
+    if not oldpid:
+        os.unlink(_pidname)
+        return  # invalid pidfile, ok
+    oldpid = int(oldpid.strip() or 0)
+    if oldpid <= 0:
+        os.unlink(_pidname)
+        return  # invalid pidfile, ok
+    try:
+        os.kill(oldpid, 0)
+    except OSError, e:
+        if e.errno == errno.ESRCH:
+            os.unlink(_pidname)
+            return  # outdated pidfile, ok
+        elif e.errno == errno.EPERM:
+            pass
+        else:
+            raise
+    raise Fatal("%s: sshuttle is already running (pid=%d)"
+                % (_pidname, oldpid))
+
+
+def daemonize():
+    if os.fork():
+        os._exit(0)
+    os.setsid()
+    if os.fork():
+        os._exit(0)
+
+    outfd = os.open(_pidname, os.O_WRONLY|os.O_CREAT|os.O_EXCL, 0666)
+    try:
+        os.write(outfd, '%d\n' % os.getpid())
+    finally:
+        os.close(outfd)
+    os.chdir("/")
+
+    # Normal exit when killed, or try/finally won't work and the pidfile won't
+    # be deleted.
+    signal.signal(signal.SIGTERM, got_signal)
+    
+    si = open('/dev/null', 'r+')
+    os.dup2(si.fileno(), 0)
+    si.close()
+
+    stderr_to_syslog()
+    log('daemonizing (%s).\n' % _pidname)
+
+
+def daemon_cleanup():
+    try:
+        os.unlink(_pidname)
+    except OSError, e:
+        if e.errno == errno.ENOENT:
+            pass
+        else:
+            raise
+
 
 def original_dst(sock):
     try:
@@ -98,11 +185,9 @@ class FirewallClient:
         if rv:
             raise Fatal('cleanup: %r returned %d' % (self.argv, rv))
 
-def exit_cleanup():
-    debug1('exit cleanup\n')
-    os.unlink('sshuttle.pid')
 
-def _main(listener, fw, ssh_cmd, remotename, python, seed_hosts, auto_nets, background):
+def _main(listener, fw, ssh_cmd, remotename, python, seed_hosts, auto_nets,
+          syslog, daemon):
     handlers = []
     if helpers.verbose >= 1:
         helpers.logprefix = 'c : '
@@ -110,30 +195,9 @@ def _main(listener, fw, ssh_cmd, remotename, python, seed_hosts, auto_nets, back
         helpers.logprefix = 'client: '
     debug1('connecting to server...\n')
 
-    if background:
-        helpers.do_syslog = True
-        syslog.openlog('sshuttle')
-
-        # we're redirecting the standard outputs here early so that
-        # the stderr debug message of ssh subprocess would be
-        # redirected properly 
-
-        # TODO: redirecting stderr of ssh to syslog
-
-        sys.stdout.flush()
-        sys.stderr.flush()
-        si = file('/dev/null', 'r')
-        so = file('/dev/null', 'a+')
-        se = file('/dev/null', 'a+', 0)
-        os.dup2(si.fileno(), sys.stdin.fileno())
-        os.dup2(so.fileno(), sys.stdout.fileno())
-        os.dup2(se.fileno(), sys.stderr.fileno())
-        si.close()
-        so.close()
-        se.close()
-
     try:
-        (serverproc, serversock) = ssh.connect(ssh_cmd, remotename, python)
+        (serverproc, serversock) = ssh.connect(ssh_cmd, remotename, python,
+                                               stderr=_loggerp.stdin)
     except socket.error, e:
         if e.errno == errno.EPIPE:
             raise Fatal("failed to establish ssh session")
@@ -153,22 +217,10 @@ def _main(listener, fw, ssh_cmd, remotename, python, seed_hosts, auto_nets, back
         raise Fatal('expected server init string %r; got %r'
                         % (expected, initstring))
     debug1('connected.\n')
-    if background:
-        debug1('daemonizing\n')
-        if os.fork(): 
-            os._exit(0)
-        os.setsid() 
-        if os.fork(): 
-            os._exit(0)
-
-        outfd = os.open('sshuttle.pid', 
-                        os.O_WRONLY | os.O_CREAT | os.O_EXCL)
-        os.write(outfd, '%i' % os.getpid())
-        os.close(outfd)
-
-        atexit.register(exit_cleanup)
-        # Normal exit when killed, or atexit won't work
-        signal.signal(signal.SIGTERM, lambda signum, stack_frame: sys.exit(1))
+    if daemon:
+        daemonize()
+    elif syslog:
+        stderr_to_syslog()
 
     def onroutes(routestr):
         if auto_nets:
@@ -225,7 +277,15 @@ def _main(listener, fw, ssh_cmd, remotename, python, seed_hosts, auto_nets, back
 
 
 def main(listenip, ssh_cmd, remotename, python, seed_hosts, auto_nets,
-         subnets_include, subnets_exclude, background):
+         subnets_include, subnets_exclude, syslog, daemon, pidfile):
+    if syslog:
+        start_syslog()
+    if daemon:
+        try:
+            check_daemon(pidfile)
+        except Fatal, e:
+            log("%s\n" % e)
+            return 5
     debug1('Starting sshuttle proxy.\n')
     listener = socket.socket()
     listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
@@ -256,6 +316,13 @@ def main(listenip, ssh_cmd, remotename, python, seed_hosts, auto_nets,
     
     try:
         return _main(listener, fw, ssh_cmd, remotename,
-                     python, seed_hosts, auto_nets, background)
+                     python, seed_hosts, auto_nets, syslog, daemon)
     finally:
-        fw.done()
+        try:
+            if daemon:
+                # it's not our child anymore; can't waitpid
+                fw.p.returncode = 0
+            fw.done()
+        finally:
+            if daemon:
+                daemon_cleanup()