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  • Adding a New Disk to a Linux Server and Creating an LVM Partition
    10/20/2017 1:43PM
    There are a number of tutorials online for adding a new disk to a machine and then extending an existing LVM partition to use the new device.

    This particular tutorial covers the use case of adding a new disk to a Linux server and then creating a NEW LVM partition on it without modifying the existing devices and LVM partitions.

    The first thing you will need to do is add the physical device to the server (or VM).

    Then, you need to confirm that the OS can 'see' the device.  The following command will show you the list of avaiable disk devices.

    # fdisk -l

    Disk /dev/sdb: 80.5 GB, 80530636800 bytes, 157286400 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes


    Here, we see that the OS can 'see' the /dev/sdb device.  For the rest of this tutorial, we will assume that your new device is /dev/sdb.

    Using fdisk, create a primary partition on the new device

    # fdisk /dev/sdb
    Welcome to fdisk (util-linux 2.23.2).

    Changes will remain in memory only, until you decide to write them.
    Be careful before using the write command.

    Device does not contain a recognized partition table
    Building a new DOS disklabel with disk identifier 0xc78ce5fd.

    Command (m for help): n
    Partition type:
       p   primary (0 primary, 0 extended, 4 free)
       e   extended
    Select (default p): p
    Partition number (1-4, default 1):
    First sector (2048-157286399, default 2048):
    Using default value 2048
    Last sector, +sectors or +size{K,M,G} (2048-157286399, default 157286399):
    Using default value 157286399
    Partition 1 of type Linux and of size 75 GiB is set

    Command (m for help): w
    The partition table has been altered!

    Calling ioctl() to re-read partition table.
    Syncing disks.


    After partitioning re-run fdisk to list the partitions

    # fdisk -l

    Disk /dev/sdb: 80.5 GB, 80530636800 bytes, 157286400 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk label type: dos
    Disk identifier: 0xc78ce5fd

       Device Boot      Start         End      Blocks   Id  System
    /dev/sdb1            2048   157286399    78642176   83  Linux


    Now, create an LVM Physical Volume (PV)

    # pvcreate /dev/sdb1
      Physical volume "/dev/sdb1" successfully created.


    Create the LVM Volume Group (VG)

    # vgcreate centos_repos /dev/sdb1
      Volume group "centos_repos" successfully created


    Execute the vgdisplay command to list all of the Volume Groups

    # vgdisplay

      --- Volume group ---
      VG Name               centos_repos
      System ID             
      Format                lvm2
      Metadata Areas        1
      Metadata Sequence No  1
      VG Access             read/write
      VG Status             resizable
      MAX LV                0
      Cur LV                0
      Open LV               0
      Max PV                0
      Cur PV                1
      Act PV                1
      VG Size               75.00 GiB
      PE Size               4.00 MiB
      Total PE              19199
      Alloc PE / Size       0 / 0   
      Free  PE / Size       19199 / 75.00 GiB
      VG UUID               FDgd3y-keqV-riq6-vb46-C2F5-JJa2-Ew2DW4


    Create a LVM Logical Volume (LV).  In this case I am going to use the entire drive

    # lvcreate -n repos --size 74.9G centos_repos
      Rounding up size to full physical extent 74.90 GiB
      Logical volume "repos" created.


    lvdisplay will list all of the existing Logical Volumes

    # lvdisplay
    ...
      --- Logical volume ---
      LV Path                /dev/centos_repos/repos
      LV Name                repos
      VG Name                centos_repos
      LV UUID                pvNLX4-3wTf-2eMY-RebF-WnFU-8y9F-BRidMn
      LV Write Access        read/write
      LV Creation host, time nebula, 2017-10-20 17:36:38 +0000
      LV Status              available
      # open                 0
      LV Size                74.90 GiB
      Current LE             19175
      Segments               1
      Allocation             inherit
      Read ahead sectors     auto
      - currently set to     8192
      Block device           253:4


    Now we need to format the LV.  In this case we will use ext4, you may choose another filesystem format.  Be sure to use the LV Path returned by lvdisplay.

    # mkfs.ext4 /dev/centos_repos/repos
    mke2fs 1.42.9 (28-Dec-2013)
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    Stride=0 blocks, Stripe width=0 blocks
    4915200 inodes, 19635200 blocks
    981760 blocks (5.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=2168455168
    600 block groups
    32768 blocks per group, 32768 fragments per group
    8192 inodes per group
    Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000, 7962624, 11239424

    Allocating group tables: done                            
    Writing inode tables: done                            
    Creating journal (32768 blocks): done
    Writing superblocks and filesystem accounting information: done   


    Now you can mount the file system as usual and/or add it to /etc/fstab.

  • [SOLVED] Unable to Customize Keyboard Shortcuts for Switching Between More Than 4 Workspaces in GNOME on CentOS 7 or RHEL 7
    08/22/2017 6:02PM
    I am working on a VM that is running GNOME under RHEL 7 and I typically run with 12 workspaces.  The default GNOME install only has the keyboard shortcut configurations up to "Switch to workspace 4".

    It turns out that the solutions is to use the gsettings cli tool to add additional shorcuts.

    $ gsettings set org.gnome.desktop.wm.keybindings switch-to-workspace-5 "[\"<Control>F5\"]"
    $ gsettings set org.gnome.desktop.wm.keybindings move-to-workspace-5 "[\"<Alt>5\"]"
  • How to See SELinux Denials That Do Not Show In the audit.log
    07/20/2017 4:43PM
    Or, otherwise know as: SELinux and Silent Denials.

    Sometimes when troubleshooting SELinux issues, you will have added new policies for each of the denial causes written to the audit.log, but SELinux will still be denying access . . . and not giving you any further information about it in the audit.log.

    Various processes often execute additional system calls that are above an beyond what they need to do for normal operation.  Many of them are blocked, and in order to keep filling the audit.log with harmless denials they are silently dropped.  These are defined by a set of dontaudit rules.

    In order to temporarily disable them, issue the following command as root

    # semodule -DB

    The -D option disables dontaudit rules and the B option will rebuild the policy.  After this runs, you should see additional information in the auditlog and with that information use audit2allow -i input-file -M output-file to build your .te and .pp files.

    After debugging is complete run the following to re-enable the dontaudit rules.

    # semodule -B
  • Mounting a Samba Share From Linux Client to Linux Samba Server
    06/02/2017 10:49PM

    In order to be able to access a Samba share on a remote client as a mounted file system execute the following command, as root on the client:

    mount -t cifs -o user=<user-on-samba-share>,uid=<uid-on-local-macheine>,gid=<gid-on-local-machine>,rw,workgroup=<your-workgroup> //ip/share /mnt/mount-point-dir

    You will be prompted for the password for the user defined on the Samba server.

    If you are able to authenticate, and then get the following error:

    ls: reading directory .: Permission denied

    Check the SELinux context type of the directory on the samba share.  It should be samba_share_t

  • Mocking Static Methods That Return void in Java
    05/11/2017 9:29AM
    This is one of those things that I tend to do on a regular basis . . . but unfortunately don't remember the details each time, so I am adding it for future reference.

    Often, developers will want to mock static methods that return void.  The Mockito and PowerMockito frameworks provide for this, but the syntax isn't immediately obvious.

    Following is an example.


    public class SomeClass {
        public static void doSomething(String arg1, int arg2) {
            // Method that does something...
        }
    }


    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.mockito.Mockito;
    import org.powermock.api.mockito.PowerMockito;
    import org.powermock.core.classloader.annotations.PowerMockIgnore;
    import org.powermock.core.classloader.annotations.PrepareForTest;
    import org.powermock.modules.junit4.PowerMockRunner;

    /*
     * The RunWith and PrepareForTest annotations are following annotations are
     * necessary to mock the static methods in the SomeClass class. The RunWith
     * enables the class to be run via PowerMock, and the PrepareForTest is an array
     * of the classes with static members that we want to mock.
     *
     * The PowerMockIgnore annotation tells PowerMock to defer the loading of
     * classes with the names supplied to the system classloader.  This will vary
     * depending on the dependency tree that you are using/testing.  It is also
     * not necessary, but here for example purposes.
     */
    @RunWith(PowerMockRunner.class)
    @PowerMockIgnore({
        "javax.management.*",
        "javax.net.ssl.*",
        "org.apache.log4j.*"
    })
    @PrepareForTest({ StatsClass.class })
    public class SomeTestClass {

        @Test
        public void shouldDoSomethingExpected() throws Exception {

            // Set up the SomeClass's static members for mocking
            PowerMockito.mockStatic(SomeClass.class);

            // Configure the mock for the method in question.
            // The following syntax is what is key here
            PowerMockito.doNothing()
                .when(SomeClass.class, "doSomething", Mockito.anyString(), Mockito.anyInt());
        }
    }

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