The file mode bits is a single character that specifies whether an alternate access method such as an access control list applies to the file.
Archive for the ‘OS Internals’ Category
important uses of LSOF Command – lsof is a Linux utility which lists the information about files opened by processes.LSOF is one of the powerful tool available for troubleshooting problems.
Autoconf is a set of tools which makes your project configurable and portable for running in Linux distributions. Simply, autoconf will help you to create configure script and Makefile for your code. Before going to generate configure script using autoconf, we need to define set of rules and dependencies. We are defining that rules and dependencies in two files, configure.in and Makefile.in. Create default Makefile and keep in project directory.We can genarate the configure.in based on the rules specified in [...]
The basic network discovery always start with ping utility.So blocking the ping requests will make the system discovery difficult.To disable ping requests ,we just need to add/modify some kernel parameters. What we are doing here is the permanent change. So open /etc/sysctl.conf and add the following line to /etc/sysctl.conf net.ipv4.icmp_echo_ignore_all = 1 And reload kernel parameters using command sysctl -p (sysctl -p is used to reload kernel parameters at runtime). After successful configuration,if any one try to ping your server [...]
Building a centralized log host in your network will ease the process of troubleshooting your servers from a single window.Centralized log host will accepts all the log messages from client and store in that server.
Environment variables in Unix are a set of dynamic named values that can affect the way running processes will be have on a computer
What is run level in Unix??? Run level defines the predefined set of operational state for Unix system.The operational state is defined in file inittab which is located in /etc. init command used to switch between different run levels.init command followed by runlevel will switch system to corresponding runlevel Eg: init 3 This will switch system to run level 3 which is text mode. Standard Linux distributions have the following run levels: No Name Description 0 Halt System will go [...]
First runlevel for Linux system which only one user is allowed to access that root user.Single user mode is useful for fixing some system problem like filesystem errors,recovering root password etc.So these are the steps for entering to single user mode in Linux.This is based on redhat enterprise linux 5( RHEL 5) Steps: Press any key during booting to go to OS listing Hit ‘e‘ to edit the selected command in the boot sequence(Read the specified instructions in bottom of [...]
First we need to find out which disks and partitions are being used. So we could use the following commands #df -h [This will display which partitions are being used] #fdisk -l [This will show which disks are being used and disks that are not mounted.] Now we can start the lvm implementation,we have two unused partitions /dev/sda3 and /dev/sda4 In logical volume creation,need to the following sequence create physical volume create volume group create logical volume 1.Create physical volume [...]
How to mark volume groups as active or inactive in Linux using lvchange command in Linux
Fencing is the disconnection of a node from the cluster’s shared storage. Fencing cuts off I/O from shared storage, thus ensuring data integrity. There are two fencing programs fenced Configured with CMAN/DLM GULM Configured with GULM servers When the cluster manager determines that a node has failed, it communicates to other cluster-infrastructure components that the node has failed. The fencing program (either fenced or GULM), when notified of the failure, fences the failed node. Other cluster-infrastructure components determine what actions [...]
Rsync: rsync is an application used in unix systems which synchronize files and directories between two machines.rsync behaves like rcp(remote file copy),but it much faster than rcp.because rsync sends the differences in the files instead of sending entire files. Servers are SERVER_SOURCE & SERVER_DESTINATION Configure SSH key authentication In SERVER_DESTINATION open sshd_config file vi /etc/ssh/sshd_config Then verify the following entries RSAAuthentication yes PubkeyAuthentication yes AuthorizedKeysFile .ssh/authorized_keys save & exit Then restart ssh daemon /etc/init.d/sshd restart Then in SERVER_SOURCE, create a [...]