Working from a Linux command line is not always intuitive, especially since there are hundreds of different commands with a myriad of switches and flags to make things even more confusing. You certainly don't need to know all of them to make good use of your Linux system, but there is a certain set of indispensable tools with which you should be familiar.
We've covered a handful of commands in previous sections that let you work with the shell and your file system. The commands covered in this section will complement what you've learned and give you some essential tools to manage your Linux environment. (You'll also be able to use these commands on other Unix-based systems.) You'll pick up other important commands in the "Text Editors" and "Slicing and Dicing" sections but you should first master this starter set to build the skills that will help you perform common Linux tasks more easily.
If You Need Help, Ask the man
Assuming you can remember the right command for a particular job, it's tougher still to remember all the switches associated with that command. The man command (short for manual) will help you on both counts by displaying pages from online manuals and telling you which commands may be relevant to the task at hand.
Say you want to change your password, but you don't know the command to do it. You can use the man command plus the keyword flag, -k, to search by keyword password for relevant commands:
man -k password
passwd passwd (1) - change login password
pwck pwck (1m) - password/group file checkers
vipw vipw (1b) - edit the password file
You can probably deduce that passwd is the correct command. But before blindly issuing any Linux command, you should know the proper syntax and understand what the command might do to you first. Using man with a command name will display all you need to know (probably more) about a command. For example, entering
passwd(1) User Commands passwd(1)
passwd - change login password and attributes
passwd [ name ]
passwd [ -d | -l ] [ -f ] [ -n min ] [ -w warn ]
[ -x max ] name
passwd -s [ -a ]
passwd -s [ name ]
The passwd command changes the password or lists
attributes associated with the user's login name.
(The man command pauses after each screenful and waits for you to press the spacebar before continuing.) The word More at the bottom of each page indicates how much of the help has so far been displayed. The terms in square brackets are optional parameters (-d, -l, -f, for example); vertical bars indicate that the terms on either side are mutually exclusive--you can use only one at a time.
Post added at 12:15
Previous post was at 12:14
Changing Password :
You can use the passwd command to change your log-in password, and as you can tell from the man output shown in the preceding section, you have quite a few options. Here are some of the most common:
passwd Change your own password.
passwd sleepy Change sleepy's password.
passwd -d sleepy Delete sleepy's password.
When you enter one of these commands to change a password, you will be prompted for the old (current) password and a new password. Your new password should be at least six characters long and not too easy for someone else to guess. Oh, and writing it down on a scrap of paper taped to your monitor is not recommended either.
If you share your Linux system with multiple users, or if you have a dial-in modem attached, password security for each account is particularly important. But if you're the only one who will ever lay a finger on your system, you might want to delete your password, thus removing the need to enter it each time you log in. It's your call, but you never know when your five-year-old will wander by the keyboard!
By the way, you might get the idea from the preceding commands that users can go around changing each other's passwords at will, but that's not the case. Only a superuser (such as root) can change or delete another user's password.