The "rescan-scsi-bus.sh" can be used to scan new LUNs in a CentOS/RHEL machine. When 'rescan-scsi-bus.sh -i' is run, script execute as well a LIP_RESET (ISSUE_LIP) which may cause a disruption in I/O on the server and even cause an outage in case of a system running on heavy load. What is LIP (Loop Initialization Protocol)? LIP scans the interconnect and causes the SCSI layer to be updated to reflect the devices currently on the bus. A LIP is, essentially, a bus reset, and will cause device … [Read more...] about When to use rescan-scsi-bus.sh -i (LIP flag) in CentOS/RHEL
Linux
How to Disable rpc.quotad Service in CentOS/RHEL 6 and 7
This post explains how to disable rpc.quotad service on CentOS/RHEL 6 or 7 machines. The protocol used by rpc.rquotad is an unsecured and obsolete protocol and should be disabled. Note: This procedure can disrupt NFS clients relying on disk quotas. To avoid issues, schedule a maintenance outage and stop these NFS clients. For CentOS/RHEL 6 or earlier 1. Edit the configuration file /etc/sysconfig/nfs to have an entry which reads RQUOTAD="no". For example: # grep RQUOTAD … [Read more...] about How to Disable rpc.quotad Service in CentOS/RHEL 6 and 7
User Unable To Edit crontab, Error: “/tmp/crontab.Lm34gsJV: Permission denied”
The Problem A non-privileged user cannot edit their crontab file using the command "crontab -e" $ crontab -e no crontab for oracle - using an empty one /tmp/crontab.Lm34gsJV: Permission denied $ The Solution This can happen mainly due to wrong permission on /tmp directory. When a user tries to edit the crontab using 'crontab -e' command, a temporary crontab file is created in /tmp directory, which is overwritten on the actual crontab file when the user saves the changes. Incorrect … [Read more...] about User Unable To Edit crontab, Error: “/tmp/crontab.Lm34gsJV: Permission denied”
showmount Command Examples in Linux
showmount command shows information about an NFS server. This information is maintained by the mountd server on the host. The default value for the host is the value returned by the hostname. With no options, show the clients that have mounted directories from the host. showmount is usually found in /usr/sbin, which is not in the default search path. showmount Command Options The options available with the showmount command are as follows: OptionDescription -a, --allPrint all remote … [Read more...] about showmount Command Examples in Linux
How to Enable Debug Mode for Chronyd Service in CentOS/RHEL 8
What is Chronyd Service In CentOS/RHEL 7 and 8, the operating system's time is set on every boot based on the hardware clock, which is a small-battery driven clock located on the motherboard of your computer. Often, this clock is too inaccurate or has not been set right, therefore it's better to get your system time from a reliable source over the Internet (that uses real atomic time). The chrony daemon, chronyd, sets and maintains system time through a process of synchronization with a remote … [Read more...] about How to Enable Debug Mode for Chronyd Service in CentOS/RHEL 8
How to Recover from a Corrupted or empty /etc/mtab file in CentOS/RHEL 7
Sometimes you may get an error while running the df command saying that tat the /etc/mtab file is either corrupt or empty(removed). It may be a case that someone accidentally edited the /etc/mtab file and has incorrect data. Well, this post will help you restore your correct mtab file. What is the use of /etc/mtab file Before we begin let's see what an mtab file is. /etc/mtab is the file that maintains a list of currently mounted filesystems. So when you run a "df" command, it referes to … [Read more...] about How to Recover from a Corrupted or empty /etc/mtab file in CentOS/RHEL 7
File Access Commands in Linux – find, sort, head, tail
The following file access commands are UNIX commands, not specific shell commands. CommandRemakr findFinds the location of a file sortReads a file and sort the output hear or tailLooks at just the start or end of a file The find Command The find command allows you to search for files and directories and to execute commands on those files. The syntax of the find command has three general argument sections. The paths section is a list of pathnames (directories) to search. The … [Read more...] about File Access Commands in Linux – find, sort, head, tail
Status Commands in Linux – date, ps, who, uptime, finger, rup, ruser
The status commands are UNIX commands, not specific shell commands. CommandPurpose dateDisplays the current (system) date and time psDisplays information about system processes whoDisplay which users are logged in to the system rusersDisplays the users on local area network (LAN) systems fingerDisplays information about logged-in users uptimeDisplays how long the system has been up rupDisplays how long LAN systems have been up (uptime for all network systems) wDisplays the … [Read more...] about Status Commands in Linux – date, ps, who, uptime, finger, rup, ruser
CentOS/RHEL : Unmounting a Windows Share Fails – “device is busy”
The Problem Unable to unmount a Windows share mount point using umount command. This Windows share is not being used by any processes recently. When executing umount command, the following error is seen; umount: /data01: device is busy. (In some cases useful info about processes that use the device is found by lsof(8) or fuser(1)) The Solution The error 'umount: device is busy' means that the mount point is being held up by the server due to some reason. An lsof command is executed … [Read more...] about CentOS/RHEL : Unmounting a Windows Share Fails – “device is busy”
How to Limit/throttle rsync transfer speed in Linux
If you use the rsync utility to keep your backups synchronized between your servers or with a local machine, you might want to prevent the script from using too much bandwidth. However, rsync makes a lot of network I/O. The point of limiting bandwidth is to make sure your backup scripts don’t clog up the network connection. Naturally, limiting the amount of bandwidth your backups are using is going to make them happen more slowly, but if you can deal with that, this is the way to do … [Read more...] about How to Limit/throttle rsync transfer speed in Linux