Questions tagged [authentication]

Use this tag for questions relating to authentication mechanism (i.e. proving to the system that you are you, using passwords, keycards etc.). In general don't use this and the security tag on the same question, unless it is about the security of the authentication process.

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109 votes
3 answers
42k 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 ...
  • 19.7k
82 votes
10 answers
212k views

Meaning of “Connection closed by xxx [preauth]” in sshd logs

We have a Windows batch script, which connects automatically to a linux server via PLINK (putty). There is NO public private key authentication, the user and the password are in the script. On our ...
73 votes
5 answers
122k views

Allow user1 to "su - user2" without password

I need to allow user martin to switch to user martin-test without password su - martin-test I think this can be configured in /etc/pam.d/su. There are already some lines in that file which can be ...
70 votes
7 answers
80k views

Can I find out which ssh key was used to access an account?

Is it possible to find out which ssh key was used to access an account? I have an account on a server that I let several (trusted!) people have access to via ssh. I'd find it useful to be able to ...
69 votes
3 answers
140k views

Permit root to login via ssh only with key-based authentication

I have some doubts about certain ssh server configurations on /etc/ssh/sshd_config. I want the next behavior: Public key authentication is the only way to authenticate as root (no password ...
  • 2,967
67 votes
4 answers
119k views

Add a user without password but with SSH and public key

I want to add a user to Red Hat Linux that will not use a password for logging in, but instead use a public key for ssh. This would be on the command line.
66 votes
5 answers
78k views

SSH keeps skipping my pubkey and asking for a password

Every time I ssh onto my remote server, I need to provide the password. I copied my public key (id_dsa.pub) to the remote server using: ssh-copy-id -i id_dsa.pub user@server I checked it was ...
  • 761
52 votes
6 answers
34k views

Gmail blocking mutt

When I try to log in to gmail with mutt, it flashes a quick Webalert with a url, something like accounts.gmail.com or something. It's too quick for me to see or copy it. Then it says Login failed. ...
  • 1,101
30 votes
7 answers
53k views

Authentication is required to create a color profile

I am running a fresh install of CentOS 7 GNOME so I could RDP from Windows.  I followed the “Connect to GNOME desktop environment via XRDP” instructions, but when I connect I get an additional login ...
29 votes
3 answers
52k views

Authentication refused: bad ownership or modes for file /var/git/.ssh/authorized_keys [duplicate]

EDIT The issue as exposed here is solved (about files modes of the .ssh folder. But an other issue persists so I create a new question : > Unable to login with SSH-RSA key I can no longer ...
  • 885
24 votes
5 answers
26k views

Is the username in Unix case sensitive?

Is ssh abc@servername different from ssh Abc@servername? Does the case of the username matter in Unix? My user authenticates via LDAP.
  • 249
23 votes
5 answers
40k views

How to stop sudo PAM messages in auth.log for a specific user?

I am using Zabbix for monitoring my environment and zabbix_agentd executes as user zabbix one custom script every 60 seconds; it uses sudo to run this script as root. In /var/log/auth.log I see every ...
user avatar
22 votes
5 answers
4k views

How do I tell what program is asking for a password?

I'm getting an occasional "Authentication request" dialog from Gnome, and I don't know what program is asking or even which account it's talking about. [email redacted] is an email address of mine, ...
  • 26.1k
20 votes
2 answers
78k views

SSH authentication using gssapi-keyex or gssapi-with-mic (publickey not permitted)

My company has disabled SSH public key authentication, therefore I have to manually enter each time my password (I am not suppose to change /etc/ssh/sshd_config). However gssapi-keyex and gssapi-with-...
  • 1,210
20 votes
2 answers
15k views

PAM - required and sufficient control flag

I'm studying PAM, and I'm a bit clueless about the meaning of some combination of control flags. From the Red Hat documentation we have: required failure of such a PAM will ultimately lead to ...
  • 1,507
19 votes
2 answers
5k 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. $ ...
  • 6,718
18 votes
3 answers
103k views

I Can't login as root with su command, but I can with SSH

How is it possible that I cannot log in as root by su root or su (I get incorrect password error), but I can log in by ssh root@localhost or ssh root@my_local_IP with the same password? I'm using ...
18 votes
2 answers
104k views

How to telnet via proxy authentication?

I am behind a proxy server in my college. It uses a simple username and password authentication. And i connect to the proxy server to port 3128. now i want to telnet simply to say any website on the ...
18 votes
3 answers
14k 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 can't log in with a password. I want to add keys to its authorized_keys by using root. This is for my automated backup system.
user avatar
16 votes
3 answers
41k views

ssh remote server on some port other than 22 without password

I am usually connecting to the remote server with ssh user@server.com -p 11000 and then giving the password each time for user. How should I avoid entering the password each time I connect using ...
16 votes
1 answer
13k views

D-Bus authentication and authorization

I'm trying to set up remote access to D-Bus, and I don't understand how authentication and authorization are (not) working. I have a D-Bus server listening on an abstract socket. $ echo $...
16 votes
1 answer
23k views

running git or ssh client in docker as user: No user exists for uid

Problem: I'm trying to run a git clone myuser@server:repo.git from within a docker container. Inside the container (due to policy) I am the same user as on the docker host system (non-root) and have ...
15 votes
7 answers
66k views

vsftpd fails pam authentication

Moving a tried-and-true vsftpd configuration onto a new server with Fedora 16, I ran into a problem. All seems to go as it should, but user authentication fails. I cannot find any entry in any log ...
  • 725
15 votes
4 answers
2k views

Groups differ from the local ones when logging in remotely

We store our users in LDAP, alongside some groups that have meaning across different systems (organizational roles including wheel). There are also groups local to workstations, e.g. audio or video ...
  • 937
14 votes
7 answers
41k views

How to sign into an open Wireless Network?

I'm running Arch Linux on my netbook. My school have an open Access Point and we must sign into the network via a page which we are redirected to when we try to open whatever website if we are not ...
12 votes
5 answers
23k views

Not able to ssh in to remote machine using shell script in Crontab

Below is the script which i am trying to run, which runs without any issue for i in `seq 200 2100` do usr=(`ssh -t -t -o ConnectTimeout=60 machine$1 finger | tail -1 | awk '{print$1}'`) echo $...
user avatar
11 votes
5 answers
12k views

Does ssh send the password over the network?

Basically the entire question is in the headline: Does ssh send the password over the network? Presuming of course that login via username and password is used. I'm asking because if ssh doesn't send ...
  • 3,075
11 votes
3 answers
66k views

What is difference between pbrun and sudo command?

What is difference between pbrun and sudo command? I have seen people executing pbrun sudo su - what this means? I know su -, it will try to switch to root user. What speciality pbrun gives to sudo ...
  • 2,232
11 votes
3 answers
17k views

How can I CTRL^C out of a password prompt?

Say I started a su command, and I want to cancel it. Control+C doesn't work for su like it does for sudo... I have to finish the prompt (either by getting the password wrong enough times or by ...
  • 3,615
11 votes
1 answer
19k views

Command line printing with a Samba printer requiring authentication

Is there a way to print to a Samba printer requiring authentication by providing the credentials on the command line (e.g., with lpr)? I managed to store the credentials in GNOME Keyring and when I ...
  • 9,466
10 votes
2 answers
16k views

Why do my sshd logs show many tries on invalid ports?

My ssh daemon is setup to listen on port 2221. I have also disabled root login from ssh. I don't understand why in auth.log I see attempts to log on other ports (example with 4627 here). May 17 15:...
  • 263
10 votes
3 answers
3k views

login and su internals

I am trying to understand how user permissions work in Linux. The kernel boots and starts init as root, right? Init then runs startup scripts and runs getty (agetty), again as root. Agetty just reads ...
10 votes
2 answers
9k views

system policy prevents control of network connections

When we log into a KDE seesion using X2Go client, the user is greeted with a dialog asking for a sudo password. I do not want the user to have a sudo password and I would like to prevent the dialog ...
  • 16k
9 votes
4 answers
4k views

How does Linux identify users?

I mean, if two users have the same name, how does the system know that they're actually different users when it enforces file permissions? This doubt came to my mind while I was considering to rename ...
9 votes
4 answers
9k 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 ?
  • 233
9 votes
4 answers
10k views

SSH authentication: either SSH keys or one time password

I have an Ubuntu 10.04 Linux server that I normally ssh into (from my home machine) using ssh key authentication. However, sometimes I need to ssh remotely from potentially insecure machines (like ...
9 votes
3 answers
37k views

How to configure for an Authenticating Proxy Server

My work proxy server requires authentication with the Microsoft AD domain user credentials. Everybody knows how it works: If you log in on a Windows workstation, your "Internet Explorer" browser based ...
  • 3,967
9 votes
3 answers
2k views

How can I lock my own account from remote ssh login with password?

I don't want to disable remote login with password altogether, but I want to make it so that my account is only accessible with key pair authentication (there are other users who wants to use ...
  • 19.7k
9 votes
1 answer
279 views

How to add additional steps to login?

What I would like to achieve is an interactive program that runs either before or after asking the user for the password, but won't handle over the access to the computer unless it exited with success....
  • 295
9 votes
1 answer
10k views

2 Factor Authentication in SSH using public key and PAM

I'm trying to setup 2 Factor Authentication. I want the user to login successfully if: The public private/public key matches (authentication method: publickey) or the password is correct My pam ...
  • 235
8 votes
6 answers
31k views

Unable to login with SSH-RSA key

This post is following this question : Authentication refused: bad ownership or modes for file /var/git/.ssh/authorized_keys . The issue as exposed there is solved (about files modes of the ....
  • 885
8 votes
3 answers
1k views

Trap: can't su as root, can't change group to wheel, ssh as root prohibited

Is this a trap? I made these steps in FreeBSD 10: 1) ssh as root prohibited 2) logged as user 3) su as root 4) as root chsh changed name of user "user" to "luser" 5) exit from ...
user avatar
8 votes
1 answer
12k views

basic explanation on NSS , LDAP and PAM

can anyone give me a basic explanation on what are NSS , LDAP and PAM and what they used for and what is their relationship/differences ?
8 votes
2 answers
1k views

setting sudo password different from login password

I am attempting to use PAM to use a different password for sudo than I do for logging in. I worked off of this post originally Set sudo password differently from login one Unfortunately, every time I ...
  • 381
8 votes
1 answer
3k views

Custom PAM modules and security considerations

I am writing my own PAM module that will be part of an application that I am developing, but I'm not sure exactly where to put it. My module basically does network-level authentication (with other ...
  • 7,223
8 votes
1 answer
17k views

how to pass a password with a cron job safely?

I have a site map generator script placed in this URL http://www.mydomain.com/admin/sitemapgen/ However this URL is protected with an username and a password in auth_type basic method. I need to ...
  • 203
8 votes
3 answers
4k 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 ...
  • 33.5k
8 votes
2 answers
12k views

Lenovo T440s Fingerprint reader in Fedora 20

I just got my new Lenovo T440s and installed Fedora 20 with Gnome 3 on it. Everything runs smoothly, except for the fingerprint reader. Its got a Validity VFS5011 (138a:0017) device which is not yet ...
8 votes
2 answers
2k views

Make new user able to login via ssh

I have been given a server to use for some computations. I have been given the root password and they told me to create an account for myself. I accessed the server using ssh root@host and inputing ...
  • 276
7 votes
2 answers
3k views

temporarily disable login using one specific ssh key

On my server, I have several public SSH keys in ~/.ssh/authorized_keys. I would like to temporarily block/disallow/deactivate one key. I want to prevent the user to log in using this key now. but I ...

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