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I haven't edited my sudoers, but I don't have to enter the password when running sudo in the command line. I can run any sudo command without entering the password, by just opening the terminal, even after rebooting the system, how can I stop this?

uid=1000(ktcool) gid=1000(ktcool) groups=1000(ktcool),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),1‌​24(sambashare)
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Is your user account secured with a password? – Davidson Chua Apr 20 '14 at 2:44
Also, if you entered a password a while ago, it caches for some time. – Thomas Ward Apr 20 '14 at 2:50
Which groups are you in? Use /usr/bin/id and read man sudoers. You are not root already, are you? – waltinator Apr 20 '14 at 3:36
Yes my user account is password secured. Even after several reboots the problem remains. Can any of you give me a work around to find whether I have accidentally edited my sudoers. – ktcool Apr 20 '14 at 3:42
There are some similar questions in AskUbuntu. Search in /etc/sudoers file and files in /etc/sudoers.d for lines that contain NOPASSWD. These were probably added by a program during installation. These lines should be the culprit. – Bruno Nova Jun 14 '14 at 9:34

Use visudo to edit your sudoers file and look for NOPASSWD: - that's the directive disabling the user password prompt (you NEVER have to enter the password of the target user, i.e. the root password). Simply removing that directive (including the colon at the end) should require you to re-enter your password to use sudo (unless you used it recently, then it's still cached, you can clear this using sudo -k)

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In the /etc/sudoers file, admin group should look like this %admin ALL=(ALL) ALL and root on the other hand is ALL=(ALL:ALL) ALL. Since in the output of your id command shows you belong to multiple groups, like lpadmin, check if any of them have line same as root's line. Alter those to look same as admin, save, reboot, and let us know if thigs are back to normal.

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Try sudo --list to show us the active sudo configuration for your account:

skath@beast:~$ sudo --list
Matching Defaults entries for skath on beast:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin

User skath may run the following commands on beast:
    (ALL : ALL) ALL

Check the timestamps on the cached credentials, this could help get an idea why you're not being prompted:

skath@beast:~$ sudo ls -al /var/lib/sudo/$USER/
total 20
drwx------ 2 root skath 4096 Jan 28 14:27 .
drwx------ 3 root root  4096 Jan 28 13:52 ..
-rw------- 1 root skath   40 Feb  5 16:18 1
-rw------- 1 root skath   40 Jan 28 14:51 2
-rw------- 1 root skath   40 Jan 28 13:56 tty1

Use sudo --remove-timestamp to try to wipe any cached credentials.

From man sudo:

 -K, --remove-timestamp
             Similar to the -k option, except that it removes the
             user's cached credentials entirely and may not be used
             in conjunction with a command or other option.  This
             option does not require a password.  Not all security
             policies support credential caching.

 -k, --reset-timestamp
             When used without a command, invalidates the user's
             cached credentials.  In other words, the next time sudo
             is run a password will be required.  This option does
             not require a password and was added to allow a user to
             revoke sudo permissions from a .logout file.

             When used in conjunction with a command or an option
             that may require a password, this option will cause sudo
             to ignore the user's cached credentials.  As a result,
             sudo will prompt for a password (if one is required by
             the security policy) and will not update the user's
             cached credentials.

             Not all security policies support credential caching.
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sudo -i is the way to go if you don't want to be typing a password every now and then while doing modifications in your system (or other systems), and you don't want to modify any system files. It will switch you toroot using your sudo user password, when you close the console or type exit you are back to your normal user. hopes this works , regards:)

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The problem is that he wants to type a password but his system isn't prompting for one, instead it accepts and executes his commands as if he has typed one. – hmayag Jun 16 '14 at 8:07

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