The Problem Updating the package iptables to iptables-1.4.7-16.0.3.el6, the service fails to start after a stop. # service iptables stop iptables: Setting chains to policy ACCEPT: filter [ OK ] iptables: Flushing firewall rules: [ OK ] iptables: Unloading modules: [ OK ] # service iptables start iptables: Applying firewall rules: Another app is currently holding the xtables lock. Perhaps you want to use the -w option? [FAILED] The Solution Iptables is being lock, and is creating … [Read more...] about Starting iptables Fails with Error “Another app is currently holding the xtables lock”
How to limit bandwidth or traffic for applications using iptables
The Ask The user wants to limit apache's bandwidth of incoming and outgoing traffic for each client IP addresses using iptables in the CentOS/RHEL box. How can we implement this? The Answer You can limit the bandwidth with "hashlimit" module of iptables. From the man page of "iptables" command: # man iptables ... hashlimit hashlimit uses hash buckets to express a rate-limiting match (like the limit match) for a group of connections using a single iptables rule. … [Read more...] about How to limit bandwidth or traffic for applications using iptables
How to Manually Bring up the Network or specific interface in CentOS/RHEL (without using NetworkManager or the network service)
How do I gain network access to a system for troubleshooting? The network service and/or NetworkManager service are not working. How can I bring networking up to troubleshoot further? How can I bring up an interface for the current boot only? Note: These settings are not persistent and will only work for the current boot. Leaving NetworkManager running, running ifup or ifdown, or starting/stopping/restarting the network service has the potential to change these manually-entered … [Read more...] about How to Manually Bring up the Network or specific interface in CentOS/RHEL (without using NetworkManager or the network service)
How to Verify if a Disk/Partition is in Use by Oracle ASM, was used by Oracle ASM or is never used by Oracle ASM
The below small C program will help us to identify if a Disk/Partition is still used by ASM, has been used by ASM or has not been used by ASM on Unix or Linux platforms. 1. First of all, we need to compile the below C code: #include <stdio.h> #include <fcntl.h> #define BLOCK_SIZE 4096 int main(int argc, char *argv[]) { char buf[BLOCK_SIZE]; char *fname; int fd; int count; if (argc != 2) { fprintf(stderr, "Exactly one argument … [Read more...] about How to Verify if a Disk/Partition is in Use by Oracle ASM, was used by Oracle ASM or is never used by Oracle ASM
How to Prevent NetworkManager from Modifying the /etc/resolv.conf file in CentOS/RHEL 7?
The Issue NetworkManager modifies the resolv.conf file and any manual changes there are lost. How to prevent the /etc/resolv.conf file from being overwritten by NetworkManager? The Solution Per the NetworkManager.conf man page: # man NetworkManager.conf ... dns Set the DNS (resolv.conf) processing mode. If the key is unspecified, default is used, unless /etc/resolv.conf is a symlink to /run/systemd/resolve/resolv.conf, /lib/systemd/resolv.conf or … [Read more...] about How to Prevent NetworkManager from Modifying the /etc/resolv.conf file in CentOS/RHEL 7?
How to configure logrotate for multiple httpd instances
The Issue When running multiple httpd instances on a single host (i.e. as suggested by this post) that has SELinux enabled and in enforcing mode, using a single logrotate configuration for log rotation may fail when a postrotate script similar to the following is used: postrotate /bin/systemctl reload httpd*.service > /dev/null 2>/dev/null || true endscript The "systemctl reload httpd*.service" command works from command line, however, SELinux policy prevents logrotate listing … [Read more...] about How to configure logrotate for multiple httpd instances
How to configure multiple instances of Apache (httpd) on the same server
The Ask We need to start multiple web server on the same box (CentOS/RHEL). How to implement two httpd servers on a single RHEL machine? Is it supported to run multiple instances of httpd on one RHEL system? The Answer CentOS/RHEL distributions don't inherently provid a convenient way of doing this, though it is possible to configure manually. There are different ways to configure multiple instances, one option is to: Duplicate http configuration files,pid,lockfile etc. 1. Duplicate … [Read more...] about How to configure multiple instances of Apache (httpd) on the same server
How to configure systemd to manage custom instance of httpd on RHEL 7
The Ask Once a new instance of httpd has been configured ( How do I configure multiple instances of Apache (httpd) on the same server? for a sample method of doing this configuration ) the process to create the systemd configuration would be the following: 1. Duplicate the systemd unit files of the standard httpd service: # cp -p /lib/systemd/system/httpd.service /lib/systemd/system/httpd.myinstance.service # cp -p /etc/sysconfig/httpd /etc/sysconfig/httpd.myinstance 2. Edit … [Read more...] about How to configure systemd to manage custom instance of httpd on RHEL 7
Red Hat Enterprise Linux Release Dates
The tables below list the major and minor Red Hat Enterprise Linux updates, their release dates, and the kernel versions that shipped with them. Red Hat does not generally disclose future release schedules. To find your Red Hat Enterprise Linux release please: $ cat /etc/redhat-release For Example: $ cat /etc/redhat-release Red Hat Enterprise Linux Server release 6.6 (Santiago) To find your kernel version please: $ uname -a For Example: $ uname -a Linux geeklab … [Read more...] about Red Hat Enterprise Linux Release Dates
Using cut on Linux Terminal
The cut command The cut command is most often used to select single columns of data from input separated by a single character, such as an /etc/passwd file. For example, the cut command is used to extract specified columns/characters of a piece of text, which is given as follows: -c: Specifies the filtering of characters -d: Specifies the delimiter for fields -f: Specifies the field number Cut Command Examples The following are a few examples that show the usage of the cut … [Read more...] about Using cut on Linux Terminal