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The who command – Terminal

Rohit — Tue, 20 Dec 2011 22:24:25 +0000

who is command or tool in Unix/Linux-based operating systems which enables the user to know who is currently logged in their system i.e who is on the System. If no option is supplied to this command, it will display the names of users currently logged in the system, along with their terminal, the time of login and the host from which they have logged in.

*** Note all the following information is tested on Ubuntu 11.10. We endeavor to keep the information up-to-date and correct, However, we cannot guarantee that information given on the site is accurate or up to date.

Syntax : who [options] [file]

Here file specify a path name of a file which can be supplied to give additional information. Default one is /etc/utmp.

General Output format : name [state] line time [idle] [pid] [comment]

name is user’s login name

state shows the user’s capability of writing to the terminal

line is name of the line found in /dev

time is time since user’s login

idle is time elapsed since the user’s last activity and . for this means currently the user is using the system i.e not idle

pid is user’s process id

comment comment line in inittab.

Following table shows all the available Options which you can use with who command/tool.

Option Available	Working
-a, –all	Equivalent to -b -d –login -p -r -t -T -u.
am i	Print the name of invoking user only i.e current terminal.
-b, –boot	Print the date and time of last system boot.
-d, –dead	Print the list of dead processes.
-H	Print column headings above the regular output.
-l, –login	Prints list of only those lines on which the system is waiting for someone to login i.e of system login processes.
-m	Same as who am i.
-p, –process	Print the list of currently active processes spawned by Init.
-q, –count	Print only the user names currently logged in and total number of users currently logged in.
-r, –runlevel	Print the current runlevel of Init process.
-s, –short	Print only name, line, and time. Which is the default behaviour
-t, –time	Print the last system clock change.
-u, –users	Print the list of currently logged in users.

Here are some of the working examples of this command:

who -m command
This command displays information of invoking user only. Following image illustrates this.

who -m command
who -q command
This command displays the user names currently logged in and total number of users currently logged in. In the following image, this command was run in the left terminal when other terminal was not open and in the other terminal when I logged in using other user id, it displays information about two users.

who -q command

Some other images of showing working of this command.

who command

who -b command

who -H command

who -p command

The passwd Command – Terminal

Rohit — Fri, 16 Dec 2011 22:19:36 +0000

passwd is command or tool in Unix/Linux-based operating systems which enables the user to change or configure Password of a User account. The password entered by user is run through a Key Derivation Function which converts the plain text to equivalent hash which is encrypted one. Original password is not saved anywhere for security reasons, only this hashed version of new password is stored in /etc/passwd file. Hashed version of plain text is usually calculated by using DES algorithm.

Syntax : passwd [options] [LOGIN]

Here LOGIN is the user-id whose password you want to change. If you want to change password of current user account, then there is no need to mention you user-id, but if you want to change password information of another user’s account, then you have to mention user-id.

Following table shows all the available Options which you can use to configure password of a user account with passwd command/tool.

Option Available	Working
-a, –all	report password status on all accounts can be used with -S option only
-d, –delete	delete the password for the named account
-e, –expire	force expire the password for the named account
-r, –repository REPOSITORY	change password in REPOSITORY repository Available Repositories : files, nis or nisplus.
-l, –lock	lock the password of the named account
-S, –status	report password status on the named account

Here are some of the working examples of this command

Changing the password of current account without using any option
For this you can refer to another article which can be found here.
Changing the password of current account without using any option
Type in the following command to change password for another user’s account. For this you must have Super User rights, otherwise it will show an error “You may not view or modify password information for [user-id]“. In the following example, I am changing password of the User account with user-id howtoideas.

sudo passwd howtoideas

It will ask you the password of the current account to use sudo command and then it will ask you to enter new password of the other user account twice, and then it will show you an output message as shown in following image.

Change Password of another account
Deleting password using -d option
Next time your Operating System will not ask for a password to log into this account. In the following example I am changing the deleting the password of howtoideas user account. If you want to delete password of your own account, then there is no need to add user-id at the end of command.

sudo passwd -d howtoideas

Here is an image of the tested command.

Delete Password
Forcefully expires the password of a user account using -e option
This will expire the current password of the user account and next time when this user tries to log into his account, System will ask the user to enter new password as enforced by root. Following command will expire the password of howtoideasuser account.

sudo passwd -e howtoideas

Following image shows the working of this command.

Change Password Expiration Information

In following image, I am trying to log into howtoideas account, and see Terminal is asking to change the current password as enforced by root.

Change password root enforced
Lock account password using -l option
This option will lock the user account password and user will not be able to log into his account even after providing correct information. In the following command I am locking the howtoideasuser account password.

sudo passwd -l howtoideas

Following image shows the output of upper command.

lock user account password

Now if i try to log into howtoideas account, I won’t be able to do so, even after providing correct password as shown in the following image.

Locked Account Password

Checking status of a particular account or all the accounts using -S option
This option will show the status information of a user account. The information shown is in the following order

name status mm/dd/yy min max warn

name	The login ID of the user.
status	Status of the name: PS or P = Password Enabled account LK or L = Locked NP = No Password NL = No login account
mm/dd/yy	The month date and year that the password was last changed.
min	The minimum number of days between password changes.
max	The maximum number of days the password is valid for the name.
warn	The number of days relative to max before the passwd uses pam for password management.

Following command will showing the information of howtoideas account.

sudo passwd -S howtoideas

Following image shows the output of upper command. See the L character in image after howtoideas in the output which shows that the account is locked. This is because in previous point I locked this account for example purpose.

Locked account Information

Checking status of a particular account or all the accounts using -S and -a Following command will output the password status information of all the account present in the system.

sudo passwd -S -a

Following image shows the output of upper command

Password Status Information of all user accounts

Login and Logout using login, exit, logout commands – Terminal

Rohit — Thu, 15 Dec 2011 21:19:28 +0000

If you are working on large system and the administrator has provided you just a terminal, then you can login to that workstation if you have your own user-id and password. In this example I will login to my own workstation using user-id howtoideas.

Loging In:

You can login to a workstation using following command

login [username]

example

login howtoideas

If above command is showing an error “login: Cannot possibly work without effective root”, then you need a root access to login. So, you can use the following command instead of upper command

sudo login howtoideas

System will ask you to provide password for the root account first and then for the account you want to login if you are loging in using sudo command otherwise it will ask only the password of the account you are trying to login to.

If you have provided wrong user-id or wrong password, then you will get an error “Login incorrect”.

If you have provided both user-id and password correct, then it will log you into that account as shown in following image.

Loging Out:

You can logout by pressing Ctrl key and the character d i.e by using [Ctrl + D]. This will work on most of the shell. But in some other shell programs like C Shell which use % as prompt. On those account logout command will work fine.

logout

logout - Terminal

You can also logout using exit command.

exit

exit - Terminal