new backup script, see #11

management/backup.py

@@ -0,0 +1,54 @@
+#!/usr/bin/python3
+
+# This script performs a backup of all user data:
+# 1) System services are stopped while a copy of user data is made.
+# 2) An incremental backup is made using rdiff-backup into the
+#    directory STORAGE_ROOT/backup/rdiff-history. This directory
+#    will contain the latest files plus a complete history for
+#    all prior backups.
+# 3) The stopped services are restarted.
+# 4) The backup directory is compressed into a single file using tar.
+# 5) That file is encrypted with a long password stored in backup/secret_key.txt.
+
+import os, os.path, subprocess
+
+from utils import exclusive_process, load_environment
+
+env = load_environment()
+
+exclusive_process("backup")
+
+# Ensure the backup directory exists.
+backup_dir = os.path.join(env["STORAGE_ROOT"], 'backup')
+rdiff_backup_dir = os.path.join(backup_dir, 'rdiff-history')
+os.makedirs(backup_dir, exist_ok=True)
+
+# Stop services.
+subprocess.check_call(["service", "dovecot", "stop"])
+subprocess.check_call(["service", "postfix", "stop"])
+
+# Update the backup directory which stores increments.
+try:
+	subprocess.check_call([
+		"rdiff-backup",
+		"--exclude", backup_dir,
+	 	env["STORAGE_ROOT"],
+	 	rdiff_backup_dir])
+except subprocess.CalledProcessError:
+	pass
+
+# Start services.
+subprocess.check_call(["service", "dovecot", "start"])
+subprocess.check_call(["service", "postfix", "start"])
+
+# Tar the rdiff-backup directory into a single file encrypted using the backup private key.
+os.system(
+	"tar -zcC %s . | openssl enc -aes-256-cbc -a -salt -in /dev/stdin -out %s -pass file:%s"
+	%
+	(	rdiff_backup_dir,
+		os.path.join(backup_dir, "latest.tgz.enc"),
+		os.path.join(backup_dir, "secret_key.txt"),
+	))
+
+# The backup can be decrypted with:
+# openssl enc -d -aes-256-cbc -a -in latest.tgz.enc -out /dev/stdout -pass file:secret_key.txt | tar -z

management/daemon.py

@@ -5,13 +5,11 @@ import os, os.path
 from flask import Flask, request, render_template
 app = Flask(__name__)
 
-# Load settings from /etc/mailinabox.conf.
+import utils
-env = { }
-for line in open("/etc/mailinabox.conf"): env.setdefault(*line.strip().split("=", 1))
-env["CONF_DIR"] = os.path.join(os.path.dirname(__file__), "../conf")
-
 from mailconfig import get_mail_users, add_mail_user, set_mail_password, remove_mail_user, get_mail_aliases, get_mail_domains, add_mail_alias, remove_mail_alias
 
+env = utils.load_environment()
+
 @app.route('/')
 def index():
     return render_template('index.html')

management/utils.py

@@ -0,0 +1,77 @@
+def load_environment():
+    # Load settings from /etc/mailinabox.conf.
+    import os.path
+    env = { }
+    for line in open("/etc/mailinabox.conf"): env.setdefault(*line.strip().split("=", 1))
+    env["CONF_DIR"] = os.path.join(os.path.dirname(__file__), "../conf")
+    return env
+
+def exclusive_process(name):
+    # Ensure that a process named `name` does not execute multiple
+    # times concurrently.
+    import os, sys, atexit
+    pidfile = '/var/run/mailinabox-%s.pid' % name
+    mypid = os.getpid()
+
+    # Attempt to get a lock on ourself so that the concurrency check
+    # itself is not executed in parallel.
+    with open(__file__, 'r+') as flock:
+        # Try to get a lock. This blocks until a lock is acquired. The
+        # lock is held until the flock file is closed at the end of the
+        # with block.
+        os.lockf(flock.fileno(), os.F_LOCK, 0)
+
+        # While we have a lock, look at the pid file. First attempt
+        # to write our pid to a pidfile if no file already exists there.
+        try:
+            with open(pidfile, 'x') as f:
+                # Successfully opened a new file. Since the file is new
+                # there is no concurrent process. Write our pid.
+                f.write(str(mypid))
+                atexit.register(clear_my_pid, pidfile)
+                return
+        except FileExistsError:
+            # The pid file already exixts, but it may contain a stale
+            # pid of a terminated process.
+            with open(pidfile, 'r+') as f:
+                # Read the pid in the file.
+                existing_pid = None
+                try:
+                    existing_pid = int(f.read().strip())
+                except ValueError:
+                    pass # No valid integer in the file.
+
+                # Check if the pid in it is valid.
+                if existing_pid:
+                    if is_pid_valid(existing_pid):
+                        print("Another %s is already running (pid %d)." % (name, existing_pid), file=sys.stderr)
+                        sys.exit(1)
+
+                # Write our pid.
+                f.seek(0)
+                f.write(str(mypid))
+                f.truncate()
+                atexit.register(clear_my_pid, pidfile)
+ 
+
+def clear_my_pid(pidfile):
+    import os
+    os.unlink(pidfile)
+
+
+def is_pid_valid(pid):
+    """Checks whether a pid is a valid process ID of a currently running process."""
+    # adapted from http://stackoverflow.com/questions/568271/how-to-check-if-there-exists-a-process-with-a-given-pid
+    import os, errno
+    if pid <= 0: raise ValueError('Invalid PID.')
+    try:
+        os.kill(pid, 0)
+    except OSError as err:
+        if err.errno == errno.ESRCH: # No such process
+            return False
+        elif err.errno == errno.EPERM: # Not permitted to send signal
+            return True
+        else: # EINVAL
+            raise
+    else:
+        return True

setup/management.sh

@@ -2,7 +2,13 @@
 
 source setup/functions.sh
 
-apt_install python3-flask links
+apt_install python3-flask links rdiff-backup
+
+# Create a backup directory and a random key for encrypting backups.
+mkdir -p $STORAGE_ROOT/backup
+if [ ! -f $STORAGE_ROOT/backup/secret_key.txt ]; then
+	openssl rand -base64 2048 > $STORAGE_ROOT/backup/secret_key.txt
+fi
 
 # Link the management server daemon into a well known location.
 rm -f /usr/bin/mailinabox-daemon