Questions regarding password-based authentication and password management

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44
votes
2answers
11k views

Why is there a big delay after entering a wrong password?

I notice a weird (well, according to me) thing about passwords. For example, if I type an incorrect password during login, there will be a few seconds' delay before the system tells me so. When I try ...
35
votes
9answers
2k views

How to trigger a system self destruct with a certain password is entered

How do I configure my system to destroy all personal data when a certain password is entered? The motivation behind this being NSA stuff. I imagine there being three primary usage cases. At login, ...
30
votes
2answers
3k views

Why is this random password is too simplistic/systematic?

How is the random string M1uG*xgRCthKWwjIjWc*010iSthY9buc being detected as too simplistic/systematic for a password according to passwd and cracklib-check? Try it on your machine and see echo ...
27
votes
4answers
25k views

Disable a user's login without disabling the account

Let's say I create a user named "bogus" using the adduser command. How can I make sure this user will NOT be a viable login option, without disabling the account. In short, I want the account to be ...
26
votes
3answers
2k views

Why shouldn't someone use passwords in the command line?

Why do people fear writing passwords in the command line? The history file is located in ~/.history, so it's available only to the user who executed the commands (and root).
20
votes
6answers
11k views

How do you create a user with no password?

In os X it's possible to have users without passwords. If you inspect them with dscl their password show up as *. This is used for system users such as users for databases like mysql, pgsql etc. ...
18
votes
10answers
3k views

How to create strong passwords in Linux?

I wonder how I can create strong passwords on Linux (for both normal and admin users) and if there are specific programs to do that.
16
votes
4answers
18k views

How to create SHA512 password hashes on command line

In Linux I can create a SHA1 password hash using sha1pass mypassword. Is there a similar command line tool which lets me create sha512 hashes? Same question for Bcrypt and PBKDF2.
16
votes
2answers
221 views

Typical use case for a group password

I checked more than half a century worth Unix experience and neither my colleagues, nor myself has ever set a password on a group (sg and gpasswd). What would be a typical use case for a group ...
15
votes
2answers
1k views

SSH ignores characters after correct password string?

Remote machine 10.10.10.1 has password "asdFGH12" for user named "user". I'm able to log in even if I type in password "asdFGH12dasdkjlkjasdus" or any other characters after the "asdFGH12" string. $ ...
15
votes
2answers
33k views

How do you change the root password on Debian?

I want to change the password I assigned to root on my Debian webserver to something longer and more secure. Bit of an obvious newbie question, but how do I do that? I haven’t forgotten/lost the ...
14
votes
4answers
2k views

How to make user passwords shown as a clear text in Linux?

We know that users' passwords are saved in /etc/passwd, but in an encrypted way, so even the root can't see them: jane:x:501:501::/home/jane:/bin/bash fred:x:502:502::/home/fred:/bin/bash As shown ...
14
votes
4answers
444 views

What specific vulnerabilities am I creating by disabling the sudo password?

Here are some instructions on how to disable your sudo password. These carry the following warning If you disable the sudo password for your account, you will seriously compromise the security of ...
14
votes
2answers
868 views

How long is the password for executing a command with sudo cached?

If I run a command which requires root privileges with sudo, I will be asked to enter the current user's password. After that for a while, if I execute the same sort of commands with sudo, I won't be ...
13
votes
6answers
2k views

Is there a root password on OS X and Ubuntu?

When you setup a new Ubuntu or OS X installation a user is generally created for you. On OS X it is whatever username you pick. On Ubuntu (the server version) usually the ubuntu user is created. The ...
12
votes
3answers
711 views

How can I tell *which* application is asking for access to gnome-keyring/Seahorse?

Whenever I log in on Ubuntu Lucid Lynx 10.04 I get a Seahorse/gnome-keyring prompt telling me an application wants to access my keyring. It isn't the network manager, because if I cancel the request ...
11
votes
4answers
1k views

Can you give a user account multiple passwords?

I want to assign 2 passwords to a single account. What I want to know is 1) is this possible, and 2) what are the security implications of this? The reason I want to do this is because I'm currently ...
10
votes
4answers
15k views

can we know the password for the other users if we have root access?

If a person has root access to a particular RHEL machine, will they be able to retrieve the password of the other users?
10
votes
3answers
1k views

How do I log into my Linux laptop if I have forgotten both the login and password?

How do I log into my Linux laptop if I have forgotten both the username and password?
10
votes
3answers
3k views

How can I make a user able to log in with ssh keys but not with a password?

I would like to create a user and have no password. As in you cant log in with a password. I want to add keys to its authorized_keys by using root. This is for my automated backup system.
10
votes
4answers
18k views

How to check password with Linux?

I want to check, from the linux command line, if a given cleartext password is the same of a crypted password on a /etc/shadow (I need this to authenticate web users. I'm running an embedded linux.) ...
10
votes
4answers
4k views

Command-line password manager that uses SSH key to authenticate

I'm looking for a command-line password manager, much like pwsafe, but one that features SSH key authentication. That is, I'd like to be able to add my SSH key to the authentication when opening the ...
9
votes
3answers
5k views

Simplest way to password protect a directory and its contents without having to create new files?

I would like to password protect or encrypt a directory and all the files within it (for the whole directory tree below it). I do not want to bother the whole home directory, I want a specific ...
8
votes
3answers
9k views

passwordless ssh for another username?

I want to do a passwordless ssh connection for a subversion project. Right now I'm using ssh+svn, and it's a little annoying, because I have to type the password any time I want to transact with the ...
8
votes
1answer
4k views

What methods are used to encrypt passwords in /etc/passwd and /etc/shadow?

A careful examination of the /etc/passwd and /etc/shadow files reveal that the passwords stored are hashed using some form of hashing function. A quick Google search reveals that by default, the ...
8
votes
1answer
2k views

In /etc/group what is the meaning of the second field?

A sample /etc/group file contains the following entries: root:*:0: adm:!:4:logcheck antoine:x:1000: The man pages I've read (Debian & OSX) says the second field is to store a group password. ...
8
votes
3answers
169 views

Clear / erase a mistyped password in a terminal

One thing that annoys me using Linux's terminal is when I have to type a invisble password, like when you run ssh the terminal I was wondering if there's a way to clear/erase the invisible password ...
8
votes
5answers
11k views

Can a linux user change their password without knowing the current password?

I'm setting up a few ubuntu boxes, and using opscode's chef as a configuration tool. It would be fairly easy to install public keys for each user on each of these servers, and disable password ...
8
votes
1answer
169 views

Does ssh-agent store my passphrase?

Is it possible to determine the passphrases of private keys added to ssh-agent? I'm thinking along the lines of someone with root privileges trying to find out my passphrase after I have added the ...
8
votes
3answers
7k views

Safe way to pass password for >1 programs in bash

I'm writing a bash script, and need to ask user for his password and pass it to openssl. Whilst openssl can read the password itself, I need for two runs of the program and don't want to ask the user ...
7
votes
4answers
938 views

Will there be always a pair of same UID and GID?

I have to change file/directory's ownership using chmod .I know only owners's username but want to change default group name simultaneosly . At this stage group name is not decided so I am putting ...
7
votes
7answers
1k views

Is there a way to store Firefox passwords in a local encrypted database in Linux?

I want Firefox to "remember" my passwords so I don't have to type them in; unfortunately, the built-in password manager stores them in plain text, which is too high a security risk. I'd like to find a ...
7
votes
5answers
17k views

Program for decrypt linux shadow file

Is there any program or script available for decrypt Linux shadow file ?
7
votes
2answers
3k views

Forcing sudo to prompt for a password

If I do the following: sudo su - //enter password exit exit //login again straight away sudo su - The second invocation of sudo does not request a password because even though I have logged out ...
7
votes
1answer
8k views

Manually generate password for /etc/shadow [duplicate]

I need to manually edit /etc/shadow to change the root password inside of a virtual machine image. Is there a command-line tool that takes a password and generates an /etc/shadow compatiable password ...
7
votes
2answers
560 views

Root and my password are the same

If I cat /etc/shadow I can get the encrypted passwords of root and my user. These passwords are the same (I know, bad security) for each account, but in /etc/shadow they show up as being different ...
7
votes
3answers
5k views

Getting the password expire time

Let me preface this with: I do NOT have root access available. I recently got locked out of my account because I did not know the password expiration was getting close, then elapsed. I want to add a ...
7
votes
2answers
4k views

Why is sudo telling me my password is wrong?

I recently installed OpenBSD 4.9 in my computer, so I could learn a little bit about Unix-like operating systems. I added a new user to the system called bruno. Ok. When I use the 'sudo' command, it ...
7
votes
3answers
2k views

Why does my sudo ask for password only once but evaluate thrice?

$ sudo some_command Password: Sorry, try again. Sorry, try again. Sorry, try again. sudo: 3 incorrect password attempts $ This is what my shell prints when I enter a wrong password to a sudoed ...
7
votes
4answers
1k views

How to set up two-factor authentication with OTP on FreeBSD?

I have a FreeBSD hosted server that I like to be able to get to from anywhere. Normally I use SSH publickey to log in, or if I don't have my SSH private key available then I might use regular password ...
6
votes
5answers
8k views

Can I change root password by sudo, without su?

I can sudo, but I don't have the root password so I can't su root. Using sudo, can I change the root password?
6
votes
3answers
40k views

How can we change root password?

If we don't know the root password and don't have root access to the machine, how can we change the root password?
6
votes
2answers
2k views

Reading passwords without showing on screen in Bash Scripts

How to read passwords in bash scripts in a way like tools which are not showing it on terminal ? (Changing font to black on black might be tricky by easy to copy&paste - so it's not solution)
6
votes
4answers
1k views

Is it possible to change password database file(/etc/passwd) in linux?

Is it possible to change password database file(/etc/passwd) to some other file. How does this authentication mechanism work internally ? Does it depend on pam ?
6
votes
1answer
323 views

How can I prevent someone from gaining root access through the bootloader?

On Ubuntu 10.10 I can login as root without the root password by replacing ro quiet splash with rw init=/bin/bash. How can I secure my machine and disable this backdoor?
6
votes
3answers
10k views

How to get back sudo on Ubuntu?

I have done this: sudo chown -R myname /usr/ and now I can't use the sudo command because of this error: sudo: must be setuid root And as I read this means that the owner of this file ...
6
votes
2answers
838 views

Pipe Password to Application When Asked

The following should be done in a bash script: curl --digest --user schmijos https://bitbucket.org/u/p/get/tip.zip -o tip.zip How can I automatically submit a password to curl when it asks for it? ...
6
votes
2answers
279 views

“no such user” but user is in passwd file

Looking at the files in /etc/: /etc/group:lbutler:*:1005: /etc/master.passwd:lbutler:$6$s..../:1005:1005::0:0:L Butler:/home/lbutler:/bin/bash /etc/passwd:lbutler:*:1005:1005:L ...
6
votes
3answers
145 views

Passwords for newly created users?

I am fairly new to Linux and I have question regarding users. When I use the useradd command I don't specify a password. I must use the passwd command afterwards. Does this mean that the user is ...
6
votes
1answer
150 views

Why do we need an expiration period?

Why is there a gap between the expiration of an account and its complete deactivation, when one can no longer log in or change his password when it became expired?