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Add lxc-start-ephemeral
This commit adds lxc-start-ephemeral as a python script using the new python-lxc API. This script is somewhat similar to lxc-clone except that it uses overlayfs or aufs to provide an overlay on top of the source container. It also allows the user to directly run a command in the container using SSH and can fetch the IP address from the container when starting the container in the background. The initial work on lxc-start-ephemeral was done by Serge Hallyn in Ubuntu, this is a re-implementation of it using python and the new LXC hooks. Compared to the shell implementation, there are three notable differences: - When starting without a command, lxc-start-ephemeral now attaches to tty1 - When starting in the background (-d), the name and IP of the container is shown on screen. - A new "-k" option is added, allowing the user to keep the ephemeral container after shutdown. This turns off the tmpfs backend and sets up the hooks so that the container can be started/stopped multiple times. Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
This commit is contained in:
Stéphane Graber
parent
697fa6390c
commit
d7415aea48
@ -97,6 +97,10 @@ bin_SCRIPTS = \
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lxc-shutdown \
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lxc-destroy
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if ENABLE_PYTHON
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bin_SCRIPTS += lxc-start-ephemeral
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endif
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bin_PROGRAMS = \
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lxc-attach \
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lxc-unshare \
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290
src/lxc/lxc-start-ephemeral
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290
src/lxc/lxc-start-ephemeral
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@ -0,0 +1,290 @@
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#!/usr/bin/python3
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#
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# lxc-start-ephemeral: Start a copy of a container using an overlay
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#
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# This python implementation is based on the work done in the original
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# shell implementation done by Serge Hallyn in Ubuntu (and other contributors)
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#
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# (C) Copyright Canonical Ltd. 2012
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#
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# Authors:
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# Stéphane Graber <stgraber@ubuntu.com>
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#
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# NOTE: To remove once the API is stabilized
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import warnings
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warnings.filterwarnings("ignore", "The python-lxc API isn't yet stable")
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import argparse
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import gettext
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import lxc
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import os
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import sys
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import subprocess
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import tempfile
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_ = gettext.gettext
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gettext.textdomain("lxc-start-ephemeral")
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# Other functions
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def randomMAC():
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import random
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mac = [0x00, 0x16, 0x3e,
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random.randint(0x00, 0x7f),
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random.randint(0x00, 0xff),
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random.randint(0x00, 0xff)]
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return ':'.join(map(lambda x: "%02x" % x, mac))
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# Begin parsing the command line
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parser = argparse.ArgumentParser(
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description=_("LXC: Start an ephemeral container"),
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formatter_class=argparse.RawTextHelpFormatter, epilog=_(
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"""If a COMMAND is given, then the container will run only as long
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as the command runs.
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If no COMMAND is given, this command will attach to tty1 and stop the
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container when exiting (with ctrl-a-q).
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If no COMMAND is given and -d is used, the name and IP addresses of the
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container will be printed to the console."""))
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parser.add_argument("--orig", "-o", type=str, required=True,
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help=_("name of the original container"))
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parser.add_argument("--bdir", "-b", type=str,
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help=_("directory to bind mount into container"))
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parser.add_argument("--user", "-u", type=str,
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help=_("the user to connect to the container as"))
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parser.add_argument("--key", "-S", type=str,
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help=_("the path to the SSH key to use to connect"))
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parser.add_argument("--daemon", "-d", action="store_true",
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help=_("run in the background"))
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parser.add_argument("--union-type", "-U", type=str, default="overlayfs",
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choices=("overlayfs", "aufs"),
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help=_("type of union (overlayfs or aufs), defaults to overlayfs."))
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parser.add_argument("--keep-data", "-k", action="store_true",
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help=_("Use a persistent backend instead of tmpfs."))
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parser.add_argument("command", metavar='CMD', type=str, nargs="*",
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help=_("Run specific command in container (command as argument)"))
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args = parser.parse_args()
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# Basic requirements check
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## Check that -d and CMD aren't used at the same time
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if args.command and args.daemon:
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print(_("You can't use -d and a command at the same time."))
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sys.exit(1)
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## The user needs to be uid 0
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if not os.geteuid() == 0:
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print(_("You must be root to run this script. Try running: sudo %s" %
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(sys.argv[0])))
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sys.exit(1)
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# Load the orig container
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orig = lxc.Container(args.orig)
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if not orig.defined:
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print(_("Source container '%s' doesn't exist." % args.orig))
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sys.exit(1)
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# Create the new container paths
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dest_path = tempfile.mkdtemp(prefix="%s-" % args.orig, dir="/var/lib/lxc/")
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os.mkdir(os.path.join(dest_path, "rootfs"))
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# Setup the new container's configuration
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dest = lxc.Container(os.path.basename(dest_path))
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dest.load_config(orig.config_file_name)
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dest.set_config_item("lxc.utsname", dest.name)
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dest.set_config_item("lxc.rootfs", os.path.join(dest_path, "rootfs"))
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dest.set_config_item("lxc.network.hwaddr", randomMAC())
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overlay_dirs = [(orig.get_config_item("lxc.rootfs"), "%s/rootfs/" % dest_path)]
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# Generate a new fstab
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if orig.get_config_item("lxc.mount"):
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dest.set_config_item("lxc.mount", os.path.join(dest_path, "fstab"))
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with open(orig.get_config_item("lxc.mount"), "r") as orig_fd:
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with open(dest.get_config_item("lxc.mount"), "w+") as dest_fd:
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for line in orig_fd.read().split("\n"):
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# Start by replacing any reference to the container rootfs
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line.replace(orig.get_config_item("lxc.rootfs"),
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dest.get_config_item("lxc.rootfs"))
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# Skip any line that's not a bind mount
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fields = line.split()
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if len(fields) < 4:
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dest_fd.write("%s\n" % line)
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continue
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if fields[2] != "bind" and "bind" not in fields[3]:
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dest_fd.write("%s\n" % line)
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continue
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# Process any remaining line
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dest_mount = os.path.abspath(os.path.join("%s/rootfs/" % (
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dest_path), fields[1]))
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if dest_mount == os.path.abspath("%s/rootfs/%s" % (
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dest_path, args.bdir)):
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dest_fd.write("%s\n" % line)
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continue
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if "%s/rootfs/" % dest_path not in dest_mount:
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print(_(
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"Skipping mount entry '%s' as it's outside of the container rootfs.") % line)
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overlay_dirs += [(fields[0], dest_mount)]
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# Generate pre-mount script
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with open(os.path.join(dest_path, "pre-mount"), "w+") as fd:
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os.fchmod(fd.fileno(), 0o755)
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fd.write("""#!/bin/sh
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LXC_DIR="%s"
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LXC_BASE="%s"
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LXC_NAME="%s"
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""" % (dest_path, orig.name, dest.name))
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count = 0
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for entry in overlay_dirs:
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target = "%s/delta%s" % (dest_path, count)
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fd.write("mkdir -p %s %s\n" % (target, entry[1]))
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if not args.keep_data:
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fd.write("mount -n -t tmpfs none %s\n" % (target))
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if args.union_type == "overlayfs":
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fd.write("mount -n -t overlayfs"
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" -oupperdir=%s,lowerdir=%s none %s\n" % (
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target,
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entry[0],
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entry[1]))
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elif args.union_type == "aufs":
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fd.write("mount -n -t aufs "
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"-o br=${upper}=rw:${lower}=ro,noplink none %s\n" % (
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target,
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entry[0],
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entry[1]))
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count += 1
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if args.bdir:
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if not os.path.exists(args.bdir):
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print(_("Path '%s' doesn't exist, won't be bind-mounted.") %
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args.bdir)
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else:
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src_path = os.path.abspath(args.bdir)
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dst_path = "%s/rootfs/%s" % (dest_path, os.path.abspath(args.bdir))
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fd.write("mkdir -p %s\nmount -n --bind %s %s\n" % (
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dst_path, src_path, dst_path))
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fd.write("""
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[ -e $LXC_DIR/configured ] && exit 0
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for file in $LXC_DIR/rootfs/etc/hostname \\
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$LXC_DIR/rootfs/etc/hosts \\
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$LXC_DIR/rootfs/etc/sysconfig/network \\
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$LXC_DIR/rootfs/etc/sysconfig/network-scripts/ifcfg-eth0; do
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[ -f "$file" ] && sed -i -e "s/$LXC_BASE/$LXC_NAME/" $file
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done
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touch $LXC_DIR/configured
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""")
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dest.set_config_item("lxc.hook.pre-mount",
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os.path.join(dest_path, "pre-mount"))
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# Generate post-stop script
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if not args.keep_data:
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with open(os.path.join(dest_path, "post-stop"), "w+") as fd:
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os.fchmod(fd.fileno(), 0o755)
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fd.write("""#!/bin/sh
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[ -n "$1" ] && [ -d "/var/lib/lxc/$1/" ] && rm -Rf /var/lib/lxc/$1/
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""")
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dest.set_config_item("lxc.hook.post-stop",
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os.path.join(dest_path, "post-stop"))
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dest.save_config()
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# Start the container
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if not dest.start() or not dest.wait("RUNNING", timeout=5):
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print(_("The container '%s' failed to start.") % dest.name)
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dest.stop()
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if dest.defined:
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dest.destroy()
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sys.exit(1)
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# Try to get the IP addresses
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ips = dest.get_ips(timeout=5)
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# Deal with the case where we don't start a command in the container
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if not args.command:
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if args.daemon:
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print(_("""The ephemeral container is now started.
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You can enter it from the command line with: lxc-console -n %s
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The following IP addresses have be found in the container:
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%s""") % (
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dest.name,
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"\n".join([" - %s" % entry for entry in ips]
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or [" - %s" % _("No address could be found")])
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))
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sys.exit(0)
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else:
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dest.console(tty=1)
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if not dest.shutdown(timeout=5):
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dest.stop()
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sys.exit(0)
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# Now deal with the case where we want to run a command in the container
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if not ips:
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print(_("Failed to get an IP for container '%s'.") % dest.name)
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dest.stop()
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if dest.defined:
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dest.destroy()
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sys.exit(1)
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# NOTE: To replace by .attach() once the kernel supports it
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cmd = ["ssh",
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"-o", "StrictHostKeyChecking=no",
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"-o", "UserKnownHostsFile=/dev/null"]
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if args.user:
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cmd += ["-l", args.user]
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if args.key:
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cmd += ["-k", args.key]
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for ip in ips:
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ssh_cmd = cmd + [ip] + args.command
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retval = subprocess.call(ssh_cmd, universal_newlines=True)
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if retval == 255:
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print(_("SSH failed to connect, trying next IP address."))
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continue
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if retval != 0:
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print(_("Command returned with non-zero return code: %s") % retval)
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break
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# Shutdown the container
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if not dest.shutdown(timeout=5):
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dest.stop()
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