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Archives for May 2018

How to allow or deny telnet login to specific users only in CentOS/RHEL

by admin

The login to specific users can be allowed or denied using the file /etc/pam.d/remote. Other network services uses the files /etc/pam.d/sshd or /etc/pam.d/password-auth for allowing or denying the access. Whereas telnet uses the file /etc/pam.d/remote. Denying telnet login to specific users 1. Add the users you want to deny the telnet login to, in the […]

Filed Under: CentOS/RHEL 5, CentOS/RHEL 6, CentOS/RHEL 7, Linux

How to Change the filesystem Labels in CentOS/RHEL

by admin

The device node name of a disk (/dev/sda, /dev/hda, /dev/vda, etc.) may change in some situations. For example, after switching cables around or upgrading certain packages, sda & sdc could swap places. This causes problems when /etc/fstab references filesystems by the disk names. Instead, we can use filesystem labels to refer them in /etc/fstab file. […]

Filed Under: CentOS/RHEL 6, CentOS/RHEL 7, Linux

How to change the default location (/var/cache/yum) of yum cache

by admin

The cachedir specifies the directory where yum stores downloaded packages, although with keepcache set to 0, yum does not store these packages after installing them. Consider a case where the /var filesystem where yum cache is located is full and there is no diskspace for yum to download the system updates. Also, you do not […]

Filed Under: CentOS/RHEL 6, CentOS/RHEL 7, Linux

How to Install and Configure Device Mapper Multipath in CentOS/RHEL 6,7

by admin

Red Hat Enterprise Linux natively supports storage that has multiple paths presented to the OS. Configuring CentOS/RHEL to use the multipath functionality is a straightforward process: Installation If not already installed, install the device-mapper-multipath package: # yum install device-mapper-multipath Location of multipath devices When devices are brought under the control of device-mapper-multipath the new multipathed […]

Filed Under: CentOS/RHEL 6, CentOS/RHEL 7, Linux

Understanding System Security Services Daemon (SSSD)

by admin

The System Security Services Daemon (SSSD) provides access to remote identity and authentication providers. Providers are configured as back ends with SSSD acting as an intermediary between local clients and any configured back-end provider. The local clients connect to SSSD and then SSSD contacts the providers. Benefits of SSSD include: Reduced load: Clients do not […]

Filed Under: CentOS/RHEL 6, CentOS/RHEL 7, Linux

How to Delete ASM Disk on Multipath Device in CentOS/RHEL

by admin

The post outlines steps to remove ASM disk on multipath device (Labeled as ASMDISK01 as an example in this post) from CentOS/RHEL server. 1. First make sure that ASM disk is no longer used by any disk group, otherwise, you might risk data integrity. The DBA can check this by using asmcmd or by logging […]

Filed Under: ASM, CentOS/RHEL 5, CentOS/RHEL 6, Linux, oracle

How to Remove a Dead Mulitpath Device without Reboot in CentOS/RHEL

by admin

Once a multipath device is down, I/O to this device is blocked. That can cause hang when collecting a sosreport or scanning/refreshing a disk. An example of a Dead Multipath device is shown below: 360060e80166bac0000016bac000000da dm-49 HITACHI,OPEN-V size=200G features=’0′ hwhandler=’0′ wp=rw ‘-+- policy=’round-robin 0′ prio=0 status=enabled |- 8:0:0:34 sdiq 135:160 failed faulty running |- 8:0:1:34 […]

Filed Under: CentOS/RHEL 5, CentOS/RHEL 6, CentOS/RHEL 7, Linux

mdadm: Cannot open /dev/sda1: Device or resource busy

by admin

The Problem When trying to re-add a device to a raid, you get the following message: # mdadm /dev/md2 –add /dev/sda1 mdadm: Cannot open /dev/sda1: Device or resource busy Whereas the mdstat command indicates that the device is inactive. # cat /proc/mdstat Personalities : md2 : inactive sda1[0](S) 292928154 blocks super 1.2 unused devices: [none] […]

Filed Under: CentOS/RHEL 6, CentOS/RHEL 7, Linux

How to set custom device names using udev in CentOS/RHEL 7

by admin

There could be a requirement from client to have custom device names such as /dev/asmdisk01 for an actual device with name /dev/sdb. Follow the steps outlined in this post to set custom device names using udev. In order to create customer name (/dev/asmdisk01p1) for /dev/sdb set udev rules as below: 1. Find UUID of device […]

Filed Under: ASM, CentOS/RHEL 7, Linux, oracle

Oracle database 12c : How to Drop Partition(s)

by admin

Dropping a Partition Dropping a partition will discard the rows stored in that partition as a DDL statement. This cannot be rolled back. It executes quickly and uses few system resources (Undo and Redo). You must be the owner of the table or have the DROP ANY TABLE privilege to drop a partition. You cannot […]

Filed Under: oracle, oracle 12c

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