What is DM-Multipath Device-Mapper Multipath (DM-Multipath) is a Linux native multipath tool, which allows you to configure multiple I/O paths between server nodes and storage arrays into a single device. These I/O paths are physical SAN connections that can include separate cables, switches, and controllers. Multipathing aggregates the I/O paths, creating a new device that consists of the aggregated paths. Beginners guide to Device Mapper (DM) multipathing Create partitions DM-Multipath … [Read more...] about How to create partitions and file systems on DM-Multipath devices
Linux
18 Practical tcpdump Command Examples – A Network Sniffer Tool Primer
What is tcpdump tcpdump is a most powerful and widely used command-line packets sniffer or package analyzer tool which is used to capture or filter TCP/IP packets that received or transferred over a network on a specific interface. It is available under most of the Linux/Unix based operating systems. tcpdump also gives us an option to save captured packets in a file for future analysis. It saves the file in a pcap format, that can be viewed by tcpdump command or an open source GUI based tool … [Read more...] about 18 Practical tcpdump Command Examples – A Network Sniffer Tool Primer
How to change the path of the auditd log file /var/log/audit/audit.log
An important task related to troubleshooting can arise from an understanding of activities commonly associated with the action of reading and writing files. Linux provides a simple utility for this. Known as auditd, this service (or daemon) starts during the boot process. Events are recorded to an associated log file found at /var/log/audit and as it runs in the background, you can check the current service status with below command in case of CentOS/RHEL 7 server: # systemctl status … [Read more...] about How to change the path of the auditd log file /var/log/audit/audit.log
How to install and configure “setroubleshootd” on CentOS/RHEL
What is setroubleshootd SELinux (Security Enhanced Linux) provides mandatory access control to the Linux operating system. SELinux is quite pervasive, even if only in PERMISSIVE mode. This can expose latent bugs in non-SELinux components that are not visible unless SELinux is running. Frustrated users have developed the perception that SELinux is difficult to use. The setroubleshoot service is intended to make SELinux more friendly. It collects SELinux audit events from the kernel and runs … [Read more...] about How to install and configure “setroubleshootd” on CentOS/RHEL
Understanding Linux SCSI Reservation
What is SCSI reservation SCSI Reservation is a mechanism which allows SCSI initiators to reserve a LUN for exclusive access and preventing other initiators from making changes. The feature is usually used in the cluster. This post elaborates the basic usage of SCSI reservation in CentOS/RHEL systems. SCSI Reservation contains two stages: First, initiators must register a reservation key, then continue to reserve the device using the same reservation key when a host need exclusive access. … [Read more...] about Understanding Linux SCSI Reservation
Linux OS Service ‘setroubleshoot’
SELinux (Security Enhanced Linux) provides mandatory access control to the Linux operating system. SELinux is quite pervasive, even if only in PERMISSIVE mode. This can expose latent bugs in non-SELinux components that are not visible unless SELinux is running. Frustrated users have developed the perception that SELinux is difficult to use. The setroubleshoot service is intended to make SELinux more friendly. It collects SELinux audit events from the kernel and runs a series of analysis … [Read more...] about Linux OS Service ‘setroubleshoot’
How to connect to an Active Directory Domain using Realmd (Configure CentOS/RHEL 7 as active directory client)
What is realmd Realmd provides a simple way to discover and join identity domains. It configures Linux system services such as sssd or winbind to do the actual network authentication and user account lookups. With the release of CentOS/RHEL 7, realmd is fully supported and can be used to join IdM, AD, or Kerberos realms. The main advantage of using realmd is the ability to provide a simple one-line command to enroll into a domain as well as configure network authentication. For example, realmd … [Read more...] about How to connect to an Active Directory Domain using Realmd (Configure CentOS/RHEL 7 as active directory client)
understanding “yum history” command output
"yum history" is an often overlooked but really useful feature provided in the CentOS/RHEL/Fedora systems. It allows you to perform a load of additional features that can save your skin in an enterprise environment. It allows you to turn back the proverbial clock to the last functioning state of an application should there be an issue with a package update, without having to worry about dependencies and so on. Shown below is an example of "yum history" command output. Understanding the … [Read more...] about understanding “yum history” command output
Linux OS Service ‘psacct’
The psacct service is responsible for starting and stopping process accounting at system boot time and at system shutdown. This service is a wrapper that invokes the action accounting control program. Service Control To obtain the psacct service, install the psacct RPM package: # yum install psacct To manage the psacct service for automated service start and stop, use the chkconfig tool: # chkconfig psacct on # chkconfig --list psacct psacct 0:off 1:off 2:on 3:on 4:on 5:on 6:off # … [Read more...] about Linux OS Service ‘psacct’
Linux OS Service ‘NetworkManagerDispatcher’
The NetworkManager daemon attempts to keep an active network connection available at all times. The NetworkManager facility offers a tool called NetworkManagerDispatcher which executes commands in /etc/NetworkManager/dispatcher.d according to the changing state of the network interfaces. All scripts in this directory are invoked for every state change of any network interface; the scripts must decide whether to process the event. The companion service NetworkManager must be running to … [Read more...] about Linux OS Service ‘NetworkManagerDispatcher’