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Preparing containers for migration

APPLIES TO:
  • Parallels Cloud Server
  • Parallels Virtuozzo Containers for Linux
  • Parallels Server

Information

This article describes steps that will help prevent migration issues. Most migration issues can be prevented by keeping OS templates up-to-date and having valid repositories for all applications and OS EZ templates.

Symptoms

A container does not start after migration. A similar error is observed:

~# vzctl start 102
Starting the Container ...
Container is mounted
Setting permissions 20002 dev 0x7d00
Set up ioprio: 4
Adding offline management to Container(1): 4643 8443 
Adding IP addresses: 10.20.30.40
Error: Unable to execute bash: No such file or directory
Container is unmounted
Failed to start the Container

There are other signs of this issue, such as the inability to show properties of the files in some directory:

CT-12264-bash-4.2# ls -al /usr/bin/ | grep '\?'
ls: cannot access /usr/bin/mailq: No such file or directory
ls: cannot access /usr/bin/hoststat: No such file or directory
ls: cannot access /usr/bin/praliases: No such file or directory
ls: cannot access /usr/bin/purgestat: No such file or directory
ls: cannot access /usr/bin/newaliases: No such file or directory
??????????  ? ?    ?              ?            ? hoststat
??????????  ? ?    ?              ?            ? mailq
??????????  ? ?    ?              ?            ? newaliases
??????????  ? ?    ?              ?            ? praliases
??????????  ? ?    ?              ?            ? purgestat
CT-12264-bash-4.2# 

Or, the following command for the mounted/started container returns some output (like find: ...: No such file or directory):

~# find /vz/root/$CTID -xdev -ls >/dev/null

(Replace "$CTID" with the actual container's ID value.)

Resolution

Before performing a migration, prepare the source and destination Hardware Nodes, as well as the container that is to be migrated:

  1. Set SCAN_PRIVATE to "yes" to assure that the vzpackages file will list all packages (and their versions) installed in the container by Virtuozzo package management tools based on existing links from the container's private area. Edit /etc/vztt/vztt.conf on both Nodes:

    ~# grep SCAN_PRIVATE /etc/vztt/vztt.conf 
    #SCAN_PRIVATE="yes"
    ~# sed -i 's/#SCAN_PRIVATE/SCAN_PRIVATE/' /etc/vztt/vztt.conf 
    ~# grep SCAN_PRIVATE /etc/vztt/vztt.conf 
    SCAN_PRIVATE="yes"
    

    NOTE: This option increases the time, required for migration. It is advised to comment it again before the migration attempt.

  2. Sync packages for the container that is to be migrated:

    ~# vzpkg sync_vzpackages $CTID
    

    (Replace "$CTID" with the actual container ID value.)

  3. It is also useful to do vzpkg repair for the migrated container if the migration failed before this step. Usually, this command is performed automatically during migration:

    ~# vzpkg repair /vz/private/$CT_ID /etc/sysconfig/vz-scripts/$CTID.conf
    

    Step 3 may return this error:

    Error: The next package(s) are not available
    

    If this happens, it means that the listed packages are missing in the template area and that these packages are not available on the configured repositories -- for example, because these packages are from an outdated OS release.

    For example, let's assume that our container is based on the centos-5-x86_64 template:

    ~# vzpkg list 113
    centos-5-x86_64      2012-04-16 15:13:10
    

    The error is as follows:

    Error: The next package(s) are not available:
    samba-swat.x86_64                        0:3.0.33-3.29.el5_5
    samba-common.x86_64                      0:3.0.33-3.29.el5_5
    glibc-common.x86_64                      2.5-49.el5_5.4
    openldap.x86_64                          2.3.43-12.el5_5.2
    krb5-libs.i386                           1.6.1-36.el5_5.5
    krb5-libs.x86_64                         1.6.1-36.el5_5.5
    nss.x86_64                               3.12.6-2.el5.centos
    glibc.i686                               2.5-49.el5_5.4
    nscd.x86_64                              2.5-49.el5_5.4
    samba.x86_64                             0:3.0.33-3.29.el5_5
    dhclient.x86_64                          12:3.0.5-23.el5_5.1
    device-mapper-multipath.x86_64           0.4.7-34.el5_5.4
    

    All missing packages above are from the Centos 5.5 release (as seen from the el5_5 part in the package version).

    Add Centos 5.5 repositories (other repositories for CentOS can be added in the same way, replacing "5.5" with the actual release ID):

    ~# echo http://vault.centos.org/5.5/os/x86_64 >> /vz/template/centos/5/x86_64/config/os/default/repositories
    ~# echo http://vault.centos.org/5.5/updates/x86_64 >> /vz/template/centos/5/x86_64/config/os/default/repositories
    

    NOTE: With many repositories in the list, the operation of metadata update (which is done every time after expiration timeout is reached, in 24 hours) takes much time to complete. It is advised to remove additional repositories when the migration is done.

    After adding/removing repositories, update metadata on the server for the EZ OS template:

    ~# vzpkg update metadata centos-5-x86_64 -r
    

    After that, vzpkg repair should be able to locate the needed packages.

    Some packages do not contain the release ID. For such packages, it is necessary to check all available repositories manually. Examples of such packages are httpd and mod_ssl.

    Digital suffixes, like .2 in .el5_5.2 version, mean that such versions are released in updates to the given release.

NOTE: The instructions above work for Parallels Cloud Server, Parallels Server Bare Metal 5.0, and Parallels Virtuozzo Containers for Linux 4.6, 4.7 with containers based on EZ OS templates.
For previous versions, these instructions work only for PSBM 4.0 (latest release) and PVCfL 4.0 starting from 4.0.0-520.
The command vzpkg repair can be used only if it is possible to create new containers based on the given OS template.

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