A TCP/IP network connection may be either blocked, dropped, open, or filtered. These actions are generally controlled by the IPtables firewall the system uses and is independent of any process or program that may be listening on a network port. Beyond the firewall, a program or process (a server or daemon) may be listening on […]
Archives for February 2017
CentOS / RHEL 6 : How to add/remove additional IP addresses to a network interface
There are two ways to add another IP address to an interface. The old way creates a new virtual interface named in the style of ethX:Y where X and Y are numbers, for instance, eth0:1. Each interface has one IP address. It appears in ifconfig output as an ordinary interface and in ip output with […]
CentOS / RHEL : How to prevent disabled repositories from being downloaded into the yum cache
Question: How to prevent disabled repositories from being downloaded into the yum cache Answer: Yum does not fetch content from disabled repositories, but the yum cache may still hold a record of these repositories. The command “yum clean all” does not try to remove content from disabled repositories. So, to entirely get rid of them, […]
Linux / UNIX OS service : autofs
Service Name autofs Description This executes auto-mount daemon for filesystem mounting. The “auto-mount” daemon “mounts a filesystem when a client sends a request to this daemon” and “unmount it when there’s no request for a long time”. There are two types of automounters in Linux, autofs and AMD. AMD is implemented in user space and […]
Linux / UNIX OS service : Bluetooth
Service Name Bluetooth Description This executes Bluetooth wireless communication daemon. Bluetooth services for service discovery, authentication, Human Interface Devices, etc. Nature The bluetooth has three daemons: # /etc/init.d/bluetooth status hcid is stopped sdpd is stopped hidd is stopped hcid – “Host Controller Interface Daemon” Manages all the Bluetooth devices. sdpd – “SDP daemon” Allows Bluetooth […]
CentOS / RHEL : How to find which user run a specific command?
Question: How can I tell which user ran a specific command ? or If the user clears their .bash_history can I still tell who ran a command? Answer: Using the process accounting tools, you can get basic information about who ran a specific command. Below are the steps to find out who run the command. […]
CentOS / RHEL 6 : How to force a NTP sync with the NTP server(s)
This post briefly outlines how one can force a ntp (Network Time Protocol) sync with the ntp servers defined in the /etc/ntp.conf configuration file. This will not work if there are no ntp servers defined in the /etc/ntp.conf, this can be verified using : # grep ^server /etc/ntp.conf This document is useful when the date […]
CentOS / RHEL : How to disable BASH shell history
Question: How to disable BASH shell history, so that it does not save users shell history? Solution: Add a line like the following to the end of /etc/profile or a new /etc/profile.d/*.sh file unset HISTFILE This will make each user’s bash shell to skip saving history files unless the users manually configure the HISTFILE variable. […]
CentOS / RHEL : How to add a null route in Linux
As Per the ip man page, there are three route types which will drop traffic in specific ways: Route types: unreachable – these destinations are unreachable. Packets are discarded and the ICMP message host unreachable is generated. The local senders get an EHOSTUNREACH error. blackhole – these destinations are unreachable. Packets are discarded silently. The […]
How to configure Kdump on SuSE Linux Enterprise System 10 and 11
The post describes how to setup kdump on SuSE Linux Enterprise System (SLES) 10 and 11 to capture core dumps from Kernel panics and crashes. Kdump (kernel dump) provides a memory dump into a file named vmcore when the kernel has critical issue. Vmcore is often required to investigate the issue. The crash dump is […]