Posts tagged Bash

How to Change Linux Account Password Through SSH: A Beginners’ Tutorial

By Eric Z Ma,
People are sometimes given access to Linux/Unix and asked to change their initial passwords. But for beginners, changing a Linux/Unix password is not an easy task, especially when there is only SSH log on allowed to the Linux/Unix server. This post introduces how to change password of user USER on host HOST remotely using SSH. linux-passwd.png Steps are as follows. Note: you will need to replace HOST and USER with the actual username and hostname you are using. » Read more

How to Force Linux to Unmount a Filesystem Reporting “device is busy”

By Eric Z Ma,
Linux may report “device is busy” when we try to umount a filesystem. This behavior is reasonable as it can help us avoid data loss by disallowing unmouting a filesystem when it is being used. But for situations when we are sure there is something wrong happened or we care not data lost such as a NFS mounting failed because that the NFS server is dead and will never be back. » Read more

Three Methods of Executing Commands on Many Nodes in Parallel via SSH on Linux

By Eric Z Ma,
It is common to execute commands on many nodes/hosts via SSH for managing a cluster of Linux servers. On Linux, there are many choices for this task. Generally, to run commands on many nodes, there are two modes: serial mode and parallel mode. In serial mode, the command is executed on the node one by one. In parallel mode, the command is executed on many nodes together. » Read more

Notes for Beginners of Software Development on Linux

By Eric Z Ma,
Linux is a great platform for software development targeting servers or backends. In general, working on Linux is very productive. The problem that beginners on Linux face is the the learning curve is steep at the beginning. But believe me, after you get through the initial green steep learning step as in the figure below with some hard work, you will feel like working on a rocket in the yellow part. » Read more

Running a Command Upon Files or Directories Changes on Linux

By Eric Z Ma,
Doing actions upon changes of files and directories is very useful. Examples like compiling a project after the source code files are changed, sending emails after important configuration files are modified, building the PDF after a TeX file is modified. On Linux, the inotify-tools provide good support for trigger actions after changes. In this post, I will introduce a small tool do-after-change.sh which continuously runs a command upon certain files and directories change. » Read more

How to Regenerate Grub2 Config Files on Linux

By Eric Z Ma,
Grub2 config file may need to be re-generated after changing Grub2 configurations such as configuration changes and setting default boot entries. The Grub2’s config file may be at different locations depending on your Linux distro and whether your Linux is booted in BIOS or UEFI mode. This makes regenerating Grub2 config file not easy for Linux users especially beginners. In this post, I will introduce a way that should be portable and easy to use. » Read more

Making Chrome Accept Self-Signed Certificates on Linux

By Eric Z Ma,
If your website uses a self-signed certificates, Chrome will show a warning every time and you need clicks to continue. In this post, I will introduce how to make Chrome accept self-signed certificates for sites on Linux. This post is made short on purpose and you need to search the Web and learn if you want to understand the stuff. self-signed-cert-chrome.png You will need libnss3-tools package on Debian/Ubuntu/Linux Mint or nss-tools on CentOS/Fedora/RHEL. » Read more

Hadoop Installation Tutorial (Hadoop 2.x)

By Eric Z Ma,
Hadoop 2 or YARN is the new version of Hadoop. It adds the yarn resource manager in addition to the HDFS and MapReduce components. Hadoop MapReduce is a programming model and software framework for writing applications, which is an open-source variant of MapReduce designed and implemented by Google initially for processing and generating large data sets. HDFS is Hadoop’s underlying data persistency layer, loosely modeled after the Google file system (GFS). » Read more

Cheatsheet: Git Branching with a Git Server

By Eric Z Ma,
It is common to set up git servers to host git repositories. Branching is lightweight in git and a very friendly mechanism to manage code. Here, I summarize a cheatsheet of common git branching commands for working on repositories from a git server. This post assumes that you have basic knowledge with git. If you are not familiar with git, you may want check Howto for New Git Users first. » Read more

Setting Up Git Commit Email Notifications

By Eric Z Ma,
A method to send email notification to a list of email addresses by the remote git server after every push from the client will be introduced in this post. An example notification email after a commit is shown in the figure below. The subject contains a prefix, the repository name, the branch name and the last commit message. The body of the email contains a summary of the changes and the commit log. » Read more

How to Set Up A Gitolite Git Server – A Ten-Minute Tutorial

By Eric Z Ma,
I ever introduced seting up git server using SSH or gitosis. However, gitolite is the way to go for managing git servers if you want an lightweight authentication layer. gitolite provides many very usefull features which can control each user’s right on each branch. I set up one gitolite git server and am very happy with it. In this post, let’s look at how to set up one gitolite git server. » Read more

Unified Linux Login and Home Directory Using OpenLDAP and NFS/automount

By Eric Z Ma,
In this post, how to unified Linux login and home directory using OpenLDAP and NFS/automount will be introduced. 0. System environment This solution is tested on Fedora 12 systems and CentOS 5. LDAP and NFS server: IP: 10.0.0.2 OS: Fedora 12 x86_64 ldap base dn: “dc=lgcpu1″ Clients: IP: 10.0.0.1/24 OS: Fedora 12 x86_64 1. LDAP server Package installation: # yum install openldap-servers # /sbin/chkconfig ldap on # /sbin/service ldap start  Add or edit these configurations: Edit /etc/openldap/slapd.conf. » Read more

Bypassing Bad fstab Failure When Booting Linux

By Eric Z Ma,
If /etc/fstab file is created with errors or the hardware configuration changes such as adding hard disks, Linux will boot into failure state. We can bypass the fstab failure by adding booting parameters to Linux. We can do this in two methods: Method 1: Boot to single user mode ∞ When booting into single user mode, Linux will not mount anything. » Read more

How to Change Linux User’s Password in One Command Line

By Eric Z Ma,
I frequently create new user accounts and change or set password for these accounts on a batch of Linux boxes. The create new user can be done by one command line. The problem is to change the password. In Linux, we use passwd to change password, but passwd requires input from stdin to get the new password. With the help of pipe and a little tricky, we can change user’s password in one command line. » Read more

Copying Output of Commands in a Linux Terminal to X Selection or Clipboard

By Eric Z Ma,
xclip is a tool to copy the copy the output of commands from a command line in a terminal to X selection or clipboard. It connects the command line interface and the X selections (clipboard) and is a very useful tool. For example, processing some text in vim in a terminal and then copying it to the browser will be easily handled by xclip. » Read more

Automatic Keyboard Presser on Linux

By Eric Z Ma,
Automatic keyboard pressers are useful tools. However, it seems that there is no simple and easy to use automatic keyboard presser for Linux if you search for “automatic keyboard presser linux”. After some digging, I find using the xvkbd with some options is a good method for automatic keyboard pressing though it is not designed for this purpose. One example ∞ Let’s use one example here to introduce how to use xvkbd as a automatic keyboard presser: we want to refresh the browser every 5 seconds to check a webpage for changes. » Read more