Archives for May 2018

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 […]

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. […]

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 […]

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 […]

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 […]

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 […]

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] […]