Sysadmin on Non-Convex Notes

A Primer to System Administration - About SSH

Fri, 29 Aug 2014 00:00:00 +0000

When we talk about SSH, we are usually referring to OpenSSH - a FREE version of the SSH connectivity tools. As their official website said:

OpenSSH encrypts all traffic (including passwords) to effectively eliminate eavesdropping, connection hijacking, and other attacks. Additionally, OpenSSH provides secure tunneling capabilities and several authentication methods, and supports all SSH protocol versions.

And I believe ssh is one of the most used commands for programmers (Windows users, you have putty, that’s … not bad). In this post I am going to list some most basic usage of ssh.

A Primer to System Administration - Know Thy System

Sun, 10 Aug 2014 00:00:00 +0000

General information

Use uname to get system information:

uname -a

-a for print all the information.

CPU information

Use nproc to print the number of processing units available (GNU coreutils):
```
$ nproc
4
```
Use lscpu to display CPU architecture information (util-linux).

Disk information

df is a powerful command for displaying system disk.
```
 df -h /path/to/directory
```
cat /proc/partitions/ and cat /proc/mounts are also pretty handly solutions to check the partitions and mount disks.

A Primer to System Administration - Users and groups

Fri, 08 Aug 2014 00:00:00 +0000

How to create a user

By useradd:

useradd -m -d <HomeDir> -g <Group> username

It’s optional to specify the new user’s home directory and group, but I strongly suggest to do so. -m stands for create home, -d to allocate a directory. (Warning, don’t mess up useradd and adduser, the later one is a higher level’s implementation. Here is a detailed explanation of these two’s differences.)

How to create a group

By groupadd: