Zone creation for dummies

This entry was posted in Solaris Administration and tagged , , on June 17, 2012, by

About Zones

In its simple form, a zone is a virtual operating system environment created within a single instance of the Solaris operating system. Efficient resource utilization is the main goal of this technology.

Solaris 10’s zone partitioning technology can be used to create local zones that behave like virtual servers. All local zones are controlled from the system’s global zone. Processes running in a zone are completely isolated from the rest of the system. This isolation prevents processes that are running in one zone from monitoring or affecting processes that are running in other zones. Note that processes running in a local zone can be monitored from global zone; but the processes running in a global zone or even in another local zone cannot be monitored from a local zone.

As of now, the upper limit for the number of zones that can be created/run on a system is 8192; of course, depending on the resource availability, a single system may or may not run all the configured zones effectively.

Global Zone

When we install Solaris 10, a global zone gets installed automatically; and the core operating system runs under global zone. To list all the configured zones, we can use zoneadm command:

% zoneadm list -v

ID NAME STATUS PATH

0 global running /
Global zone is the only one:

  • bootable from the system hardware
  • to be used for system-wide administrative control, such as physical devices, routing, or dynamic reconfiguration (DR). ie., global zone is the only zone that is aware of all devices and all file systems
  • from which a non-global zone can be configured, installed, managed, or uninstalled. ie., global zone is the only zone that is aware of the existence of non-global (local) zones and their configurations. It is not possible to create local zones, within a local zone

Steps to create a Local Zone

Prerequisites:

  • Plenty of disk space to hold the newly installed zone. It needs at least 2G space to copy the essential files to the local zone, and of course the disk space needed by the application(s) you are planning to run, in this zone; and
  • A dedicated IP, for network connectivity

Basic Zone creation steps, with examples:

  1. Check the disk space & network configuration

    % df -h /

    Filesystem size used avail capacity Mounted on

    /dev/dsk/c1t1d0s0 29G 22G 7.1G 76% /

    % ifconfig -a

    lo0: flags=2001000849 mtu 8232 index 1

    inet 127.0.0.1 netmask ff000000

    eri0: flags=1000843 mtu 1500 index 2

    inet 192.168.74.217 netmask fffffe00 broadcast 192.168.75.255

     

  2. Since there is more than 5G free space, I’ve decided to install a local zone under /zones.

    % mkdir /zones

     

  3. Next step is to define/create the zone root. This is the path to zone’s root directory that is relative to the global zone’s root directory. Zone root must be owned by root user with the mode 700. This will be used in setting the zonepath property, during the zone creation process

    % cd /zones

    % mkdir appserver

    % chmod 700 appserver

    % ls -l

    total 2

    drwx—— 2 root root 512 Feb 17 12:46 appserver

     

  4. Create & configure a new ‘sparse root’ local zone, with root privileges

    % zonecfg -z appserv

    appserv: No such zone configured

    Use ‘create’ to begin configuring a new zone.

    zonecfg:appserv> create

    zonecfg:appserv> set zonepath=/zones/appserver

    zonecfg:appserv> set autoboot=true

    zonecfg:appserv> add net

    zonecfg:appserv:net> set physical=eri0

    zonecfg:appserv:net> set address=192.168.175.126

    zonecfg:appserv:net> end

    zonecfg:appserv> add fs

    zonecfg:appserv:fs> set dir=/repo2

    zonecfg:appserv:fs> set special=/dev/dsk/c2t40d1s6

    zonecfg:appserv:fs> set raw=/dev/rdsk/c2t40d1s6

    zonecfg:appserv:fs> set type=ufs

    zonecfg:appserv:fs> set options noforcedirectio

    zonecfg:appserv:fs> end

    zonecfg:appserv> add inherit-pkg-dir

    zonecfg:appserv:inherit-pkg-dir> set dir=/opt/csw

    zonecfg:appserv:inherit-pkg-dir> end

    zonecfg:appserv> info

    zonepath: /zones/appserver

    autoboot: true

    pool:

    inherit-pkg-dir:

    dir: /lib

    inherit-pkg-dir:

    dir: /platform

    inherit-pkg-dir:

    dir: /sbin

    inherit-pkg-dir:

    dir: /usr

    inherit-pkg-dir:

    dir: /opt/csw

    net:

    address: 192.168.175.126

    physical: eri0

    zonecfg:appserv> verify

    zonecfg:appserv> commit

    zonecfg:appserv> exit
    Sparse Root Zone Vs Whole Root Zone(Updated 05/07/2008)

    In a Sparse Root Zone, the directories /usr, /sbin, /lib and /platform will be mounted as loopback file systems. That is, although all those directories appear as normal directories under the sparse root zone, they will be mounted as read-only file systems. Any change to those directories in the global zone can be seen from the sparse root zone.

    However if you need the ability to write into any of those directories listed above, you may need to configure a Whole Root Zone. For example, softwares like ClearCase need write permissions to /usr directory. In that case configuring a Whole Root Zone is the way to go. The steps for creating and configuring a new ‘Whole Root’ local zone are as follows:

    % zonecfg -z appserv

    appserv: No such zone configured

    Use ‘create’ to begin configuring a new zone.

    zonecfg:appserv> create

    zonecfg:appserv> set zonepath=/zones/appserver

    zonecfg:appserv> set autoboot=true

    zonecfg:appserv> add net

    zonecfg:appserv:net> set physical=eri0

    zonecfg:appserv:net> set address=192.168.175.126

    zonecfg:appserv:net> end

    zonecfg:appserv> add inherit-pkg-dir

    zonecfg:appserv:inherit-pkg-dir> set dir=/opt/csw

    zonecfg:appserv:inherit-pkg-dir> end

    zonecfg:appserv> remove inherit-pkg-dir dir=/usr

    zonecfg:appserv> remove inherit-pkg-dir dir=/sbin

    zonecfg:appserv> remove inherit-pkg-dir dir=/lib

    zonecfg:appserv> remove inherit-pkg-dir dir=/platform

    zonecfg:appserv> info

    zonepath: /zones/appserver

    autoboot: true

    pool:

    inherit-pkg-dir:

    dir: /opt/csw

    net:

    address: 192.168.175.126

    physical: eri0

    zonecfg:appserv> verify

    zonecfg:appserv> commit

    zonecfg:appserv> exit
    Brief explanation of the properties that I added:

    zonepath=/zones/appserver
    Local zone’s root directory, relative to global zone’s root directory. ie., local zone will have all the bin, lib, usr, dev, net, etc, var, opt etc., directories physically under /zones/appserver directory

    autoboot=true
    boot this zone automatically when the global zone is booted

    physical=eri0
    eri0 card is used for the physical interface

    address=192.168.175.126
    192.168.175.126 is the IP address. It must have all necessary DNS entries

    [Added 08/25/08] The whole add fs section adds the file system to the zone. In this example, the file system that is being exported to the zone is an existing UFS file system.

    set dir=/repo2
    /repo2 is the mount point in the local zone

    set special=/dev/dsk/c2t40d1s6
    set raw=/dev/rdsk/c2t40d1s6

    Grant access to the block (/dev/dsk/c2t40d1s6) and raw (/dev/rdsk/c2t40d1s6) devices so the file system can be mounted in the non-global zone. Make sure the block device is not mounted anywhere right before installing the non-global zone. Otherwise, the zone installation may fail with ERROR: file system check </usr/lib/fs/ufs/fsck> of </dev/rdsk/c2t40d1s6> failed: exit status <33>: run fsck manually. In that case, unmount the file system that is being exported, uninstall the partially installed zone (zoneadm -z <zone> uninstall) then install the zone from the scratch (no need to re-configure the zone, just do a re-install).

    set type=ufs
    The file system is of type UFS

    set options noforcedirectio
    Mount the file system with the option noforcedirectio[/Added 08/25/08]

    dir=/opt/csw
    read-only path, will be lofs’d (loop back mounted) from global zone. Note: it works for sparse root zone only — whole root zone cannot have any shared file systems

    zonecfg commands verify and commit, verifies and commits the zone configuration for the zone, respectively. Note that it is not necessary to commit the zone configuration; it will be done automatically when we exit from zonecfg tool. info displays information about the current configuration

  5. Check the state of the newly created/configured zone

    % zoneadm list -cv

    ID NAME STATUS PATH

    0 global running /

    – appserv configured /zones/appserver

     

  6. Next step is to install the configured zone. It takes a while to install the necessary packages

    % zoneadm -z appserv install

    /zones must not be group writable.

    could not verify zonepath /zones/appserver because of the above errors.

    zoneadm: zone appserv failed to verify

    % ls -ld /zones

    drwxrwxr-x 3 root root 512 Feb 17 12:46 /zones

    Since /zones must not be group writable, let’s change the mode to 700.

    % chmod 700 /zones

    % ls -ld /zones

    drwx—— 3 root root 512 Feb 17 12:46 /zones

    % zoneadm -z appserv install

    Preparing to install zone .

    Creating list of files to copy from the global zone.

    Copying <2658> files to the zone.

    Initializing zone product registry.

    Determining zone package initialization order.

    Preparing to initialize <1128> packages on the zone.

    Initialized <1128> packages on zone.

    Zone is initialized.

    Installation of these packages generated errors:

    Installation of <2> packages was skipped.

    Installation of these packages generated warnings: <CSWbdb3 CSWtcpwrap

    CSWreadline CSWlibnet CSWlibpcap CSWjpeg CSWzlib CSWcommon CSWpkgget SMCethr CSWxpm

    SMClsof SMClibgcc SMCossld OpenSSH SMCtar SUNWj3dmx CSWexpat CSWftype2 CSWfconfig

    CSWiconv CSWggettext CSWlibatk CSWpango CSWpng CSWtiff CSWgtk2 CSWpcre CSWlibmm

    CSWgsed CSWlibtool CSWncurses CSWunixodbc CSWoldap CSWt1lib CSWlibxml2 CSWbzip2

    CSWlibidn CSWphp>

    The file contains a log of the zone installation.

     

  7. Verify the state of the appserv zone, one more time

    % zoneadm list -cv

    ID NAME STATUS PATH

    0 global running /

    – appserv installed /zones/appserver

     

  8. Boot up the appserv zone. Let’s note down the ifconfig output to see how it changes after the local zone boots up. Also observe that there is no answer from the server yet, since it is not up

    % ping 192.168.175.126

    no answer from 192.168.175.126

    % ifconfig -a

    lo0: flags=2001000849 mtu 8232 index 1

    inet 127.0.0.1 netmask ff000000

    eri0: flags=1000843 mtu 1500 index 2

    inet 192.168.74.217 netmask fffffe00 broadcast 192.168.75.255

    ether 0:3:ba:2d:0:84

    % zoneadm -z appserv boot

    zoneadm: zone ‘appserv’: WARNING: eri0:1: no matching subnet found in netmasks(4) for 192.168.175.126;

    using default of 255.255.0.0.

    % zoneadm list -cv

    ID NAME STATUS PATH

    0 global running /

    1 appserv running /zones/appserver

    % ping 192.168.175.126

    192.168.175.126 is alive

    % ifconfig -a

    lo0: flags=2001000849 mtu 8232 index 1

    inet 127.0.0.1 netmask ff000000

    lo0:1: flags=2001000849 mtu 8232 index 1

    zone appserv

    inet 127.0.0.1 netmask ff000000

    eri0: flags=1000843 mtu 1500 index 2

    inet 192.168.74.217 netmask fffffe00 broadcast 192.168.75.255

    ether 0:3:ba:2d:0:84

    eri0:1: flags=1000843 mtu 1500 index 2

    zone appserv

    inet 192.168.175.126 netmask ffff0000 broadcast 192.168.255.255

    Observe that the zone appserv has it’s own virtual instance of lo0, the system’s loopback interface and the zone’s IP address is also being served by the eri0 network interface

  9. Login to the Zone {console} and performing the internal zone configuration. zlogin utility can be used to enter a zone. The first time we log in to the console, we get a chance to answer a series of questions for the desired zone configuraton. -C option of zlogin can be used to log in to the Zone console.

    % zlogin -C -e [ appserv

    [Connected to zone ‘appserv’ console]

    Select a Language

    0. English

    1. es

    2. fr

    Please make a choice (0 – 2), or press h or ? for help: 0

    Select a Locale

    0. English (C – 7-bit ASCII)

    1. Canada (English) (UTF-8)

    2. Canada-English (ISO8859-1)

    3. U.S.A. (UTF-8)

    4. U.S.A. (en_US.ISO8859-1)

    5. U.S.A. (en_US.ISO8859-15)

    6. Go Back to Previous Screen

    Please make a choice (0 – 6), or press h or ? for help: 0

    Enter the host name which identifies this system on the network. The name

    must be unique within your domain; creating a duplicate host name will cause

    problems on the network after you install Solaris.

    A host name must have at least one character; it can contain letters,

    digits, and minus signs (-).

    Host name for eri0:1 appserv v440appserv

    System identification is completed.

     

    rebooting system due to change(s) in /etc/default/init

     

    [NOTICE: Zone rebooting]

    SunOS Release 5.11 Version snv_23 64-bit

    Copyright 1983-2005 Sun Microsystems, Inc. All rights reserved.

    Use is subject to license terms.

    Hostname: v440appserv

    v440appserv console login: root

    Password:

    Feb 17 15:15:30 v440appserv login: ROOT LOGIN /dev/console

    Sun Microsystems Inc. SunOS 5.11 snv_23 October 2007

    %

That is all there is in the creation of a local zone. Now simply login to the newly created zone, just like connecting to any other system in the network.

[New 08/27/2008] Mounting file systems in a non-global zone

Sometimes it might be necessary to export file systems or create new file systems when the zone is already running. This section’s focus is on exporting block devices and the raw devices in such situations i.e., when the local zone is already configured.

Exporting the Raw Device(s) to a non-global zone

If the file system does not exist on the device, raw devices can be exported as they are, so the file system can be created inside the non-global zone using the normal newfs command.

The following example shows how to export the raw device to a non-global zone when the zone is already configured.

# zonecfg -z appserv

zonecfg:appserv> add device

zonecfg:appserv:device> set match=/dev/rdsk/c5t0d0s6

zonecfg:appserv:device> end

zonecfg:appserv> verify

zonecfg:appserv> commit

zonecfg:appserv> exit

In this example /dev/rdsk/c5t0d0s6 is being exported.

After the zonecfg step, reboot the non-global zone to make the raw device visible inside the non-global zone. After the reboot, check the existence of the raw device.

# hostname

v440appserv

# ls -l /dev/rdsk/c5t0d0s6

crw-r—– 1 root sys 118, 126 Aug 27 14:33 /dev/rdsk/c5t0d0s6

Now that the raw device is accessible within the non-global zone, we can use the regular Solaris commands to create any file system like UFS.

eg.,

# newfs -v c5t0d0s6

newfs: construct a new file system /dev/rdsk/c5t0d0s6: (y/n)? y

mkfs -F ufs /dev/rdsk/c5t0d0s6 1140260864 -1 -1 8192 1024 251 1 120 8192 t 0 -1 8 128 n

Warning: 4096 sector(s) in last cylinder unallocated

/dev/rdsk/c5t0d0s6: 1140260864 sectors in 185590 cylinders of 48 tracks, 128 sectors

556768.0MB in 11600 cyl groups (16 c/g, 48.00MB/g, 5824 i/g)

super-block backups (for fsck -F ufs -o b=#) at:

32, 98464, 196896, 295328, 393760, 492192, 590624, 689056, 787488, 885920,

Initializing cylinder groups:

…………………………………………………………………….

…………………………………………………………………….

……………………………………………………………….

super-block backups for last 10 cylinder groups at:

1139344160, 1139442592, 1139541024, 1139639456, 1139737888, 1139836320,

1139934752, 1140033184, 1140131616, 1140230048

Exporting the Block Device(s) to a non-global zone

If the file system exists on the device, block devices can be exported as they are, so the file system can be mounted inside the non-global zone using the normal Solaris command, mount.

The following example shows how to export the block device to a non-global zone when the zone is already configured.

# zonecfg -z appserv

zonecfg:appserv> add device

zonecfg:appserv:device> set match=/dev/dsk/c5t0d0s6

zonecfg:appserv:device> end

zonecfg:appserv> verify

zonecfg:appserv> commit

zonecfg:appserv> exit

In this example /dev/dsk/c5t0d0s6 is being exported.

After the zonecfg step, reboot the non-global zone to make the block device visible inside the non-global zone. After the reboot, check the existence of the block device; and mount the file system within the non-global zone.

# hostname

v440appserv

# ls -l /dev/dsk/c5t0d0s6

brw-r—– 1 root sys 118, 126 Aug 27 14:40 /dev/dsk/c5t0d0s6

# fstyp /dev/dsk/c5t0d0s6

ufs

# mount /dev/dsk/c5t0d0s6 /mnt

# df -h /mnt

Filesystem size used avail capacity Mounted on

/dev/dsk/c5t0d0s6 535G 64M 530G 1% /mnt

Mounting a file system from the global zone into the non-global zone

Sometimes it is desirable to have the flexibility of mounting a file system in the global zone or non-global zone on-demand. In such situations, rather than exporting the file systems or block devices into the non-global zone, create the file system in the global zone and mount the file system directly from the global zone into the non-global zone. Make sure to unmount that file system in the global zone if mounted, before attempting to mount it in the non-global zone.

eg.,
In the non-global zone:

# mkdir /repo1

In the global zone:

# df -h /repo1

/dev/dsk/c2t40d0s6 134G 64M 133G 1% /repo1

# umount /repo1

# ls -ld /zones/appserv/root/repo1

drwxr-xr-x 2 root root 512 Aug 27 14:45 /zones/appserv/root/repo1

# mount /dev/dsk/c2t40d0s6 /zones/appserv/root/repo1

Now go back to the non-global zone and check the mounted file systems.

# hostname

v440appserv

# df -h /repo1

Filesystem size used avail capacity Mounted on

/repo1 134G 64M 133G 1% /repo1

To unmount the file system from the non-global zone, run the following command from the global zone.

# umount /zones/appserv/root/repo1

Removing the file system from the non-global zone

eg.,
Earlier in the zone creation step, the block device /dev/dsk/c2t40d1s6 was exported and mounted on the mount point /repo2 inside the non-global zone. To remove the file system completely from the non-global zone, run the following in the global zone.

# zonecfg -z appserv

zonecfg:appserv> remove fs dir=/repo2

zonecfg:appserv> verify

zonecfg:appserv> commit

zonecfg:appserv> exit

Reboot the non-global zone for this setting to take effect.
[New: 08/27/2008]

Shutting down and booting up the local zones (Updated 01/15/2008)

  1. To bring down the local zone:

    % zlogin appserv shutdown -i 0

     

  2. To boot up the local zone:

    % zoneadm -z appserv boot

Just for the sake of completeness, the following steps show how to remove a local zone.

Steps to delete a Local Zone

  1. Shutdown the local zone

    % zoneadm -z appserv halt

    % zoneadm list -cv

    ID NAME STATUS PATH

    0 global running /

    – appserv installed /zones/appserver

     

  2. Uninstall the local zone — remove the root file system

    % zoneadm -z appserv uninstall

    Are you sure you want to uninstall zone appserv (y/[n])? y

    zoneadm list -cv

    ID NAME STATUS PATH

    0 global running /

    – appserv configured /zones/appserver

     

  3. Delete the configured local zone

    % zonecfg -z appserv delete

    Are you sure you want to delete zone appserv (y/[n])? y

    zoneadm list -cv

    ID NAME STATUS PATH

    0 global running /

[New: 07/14/2009]
Cloning a Non-Global Zone

The following instructions are for cloning a non-global zone on the same system. The example shown below clones the siebeldb zone. After the cloning process, a brand new zone oraclebi emerges as a replica of siebeldb zone.

eg.,

# zoneadm list -cv

ID NAME STATUS PATH BRAND IP

0 global running / native shared

– siebeldb installed /zones/dbserver native excl

 

  1. Export the configuration of the zone that you want to clone/copy

    # zonecfg -z siebeldb export > /tmp/siebeldb.config.cfg

     

  2. Change the configuration of the new zone that differ from the existing one — for example, IP address, data set names, network interface etc. To make these changes, edit /tmp/siebeldb.config.cfg
  3. Create the zone root directory for the new zone being created

    # mkdir /zones3/oraclebi

    # chmod 700 /zones3/oraclebi

    # ls -ld /zones3/oraclebi

    drwx—— 2 root root 512 Mar 12 15:41 /zones3/oraclebi

     

  4. Create a new (empty, non-configured) zone in the usual manner with the edited configuration file as an input

    # zonecfg -z oraclebi -f /tmp/siebeldb.config.cfg

    # zoneadm list -cv

    ID NAME STATUS PATH BRAND IP

    0 global running / native shared

    – siebeldb installed /zones/dbserver native excl

    – oraclebi configured /zones3/oraclebi native excl

     

  5. Ensure that the zone you intend to clone/copy is not running

    # zoneadm -z siebeldb halt

     

  6. Clone the existing zone

    # zoneadm -z oraclebi clone siebeldb

    Cloning zonepath /zones/dbserver…
    This step takes at least 5 minutes to clone the whole zone. Larger zones may take longer to complete the cloning process.

  7. Boot the newly created zone

    # zoneadm -z oraclebi boot
    Bring up the halted zone (the source zone) as well, if wish.

  8. Login to the console of the new zone to configure IP, networking, etc., and you are done.

    # zlogin -C oraclebi

[New: 07/15/2009]
Migrating a Non-Global Zone from One Host to Another

Keywords: Solaris, Non-Global Zone, Migration, Attach, Detach

The following instructions demonstrate how to migrate the non-global zone, orabi to another server with examples.

# zoneadm list -cv

ID NAME STATUS PATH BRAND IP

0 global running / native shared

4 siebeldb running /zones/dbserver native excl

– orabi installed /zones3/orabi native shared

 

  1. Halt the zone to be migrated, if running

    # zoneadm -z orabi halt

     

  2. Detach the zone. Once detached, it will be in the configured state

    # zoneadm -z orabi detach

    # zoneadm list -cv

    ID NAME STATUS PATH BRAND IP

    0 global running / native shared

    4 siebeldb running /zones/dbserver native excl

    – orabi configured /zones3/orabi native shared

     

  3. Move the zonepath for the zone to be migrated from the old host to the new host.

    Do the following on the old host:

    # cd /zones3

    # tar -Ecf orabi.tar orabi

    # compress orabi.tar

    # sftp newhost

    Connecting to newhost

    sftp> cd /zones3

    sftp> put orabi.tar.Z

    Uploading orabi.tar.Z to /zones3/orabi.tar.Z

    sftp> quit
    On the newhost:

    # cd /zones3

    # uncompress orabi.tar.Z

    # tar xf orabi.tar

     

  4. On the new host, configure the zone.

    Create the equivalent zone orabi on the new host — use the zonecfg command with the -a option and the zonepath on the new host. Make any required adjustments to the configuration and commit the configuration.

    # zonecfg -z orabi

    orabi: No such zone configured

    Use ‘create’ to begin configuring a new zone.

    zonecfg:orabi> create -a /zones3/orabi

    zonecfg:orabi> info

    zonename: orabi

    zonepath: /zones3/orabi

    brand: native

    autoboot: false

    bootargs:

    pool:

    limitpriv: all,!sys_suser_compat, !sys_res_config, !sys_net_config,!sys_linkdir, !sys_devices, !sys_config, !proc_zone, !dtrace_kernel,!sys_ip_config

    scheduling-class:

    ip-type: shared

    inherit-pkg-dir:

    dir: /lib

    inherit-pkg-dir:

    dir: /platform

    inherit-pkg-dir:

    dir: /sbin

    inherit-pkg-dir:

    dir: /usr

    net:

    address: IPaddress

    physical: nxge1

    defrouter not specified

    zonecfg:orabi> set capped-memory

    zonecfg:orabi:capped-memory> set physical=8G

    zonecfg:orabi:capped-memory> end

    zonecfg:orabi> commit

    zonecfg:orabi> exit

     

  5. Attach the zone on the new host with a validation check and update the zone to match a host running later versions of the dependent packages

    # ls -ld /zones3

    drwxrwxrwx 5 root root 512 Jul 15 12:30 /zones3

    # chmod g-w,o-w /zones3

    # ls -ld /zones3

    drwxr-xr-x 5 root root 512 Jul 15 12:30 /zones3

    # zoneadm -z orabi attach -u

    Getting the list of files to remove

    Removing 1740 files

    Remove 607 of 607 packages

    Installing 1878 files

    Add 627 of 627 packages

    Updating editable files

    The file within the zone contains a log of the zone update.

    # zoneadm list -cv

    ID NAME STATUS PATH BRAND IP

    0 global running / native shared

    – orabi installed /zones3/orabi native shared
    Note:
    It is possible to force the attach operation without performing the validation. You can do so with the help of -F option

    # zoneadm -z orabi attach -F
    Be careful when using this option because it could lead to an incorrect configuration; and an incorrect configuration could result in undefined behavior

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