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 install and start the Apache httpd service
Question: How to install Apache and configure Apache httpd to run as a service? Answer: Installing the Apache package If you have the apache package downloaded, you can install it using rpm command as root user. # rpm -ivh httpd If you have yum repository configured, use the recommended way of installing Apache httpd, i.e. […]
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 […]
CentOS / RHEL : Configure yum automatic updates with yum-cron service
yum-cron is an optional package starting from Red Hat Enterprise Linux 6, this is a plugin for yum. From man page of yum-cron : yum-cron is a simple way to call yum commands from cron. It provides configuration to keep repository metadata up to date, and to check for, download, and apply updates. The yum-cron […]
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 7 : How to open a port in the firewall with firewall-cmd?
Question: How to open a port in RHEL 7 using the firewall-cmd command? Solution: To begin with check the firewalld status using the systemctl command : # systemctl status firewalld ● firewalld.service – firewalld – dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled) Active: active (running) since Sat 2016-10-29 21:47:04 IST; 1 weeks […]
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 […]