Content related to computer security., i.e. content about policies, mechanisms, etc. needed make sure data is not leaked or corrupted and services available in all circumstances.

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3answers
496 views

Unix users, groups, and permissions

I don't understand unix users, groups, permissions, etc. For example, things managed by the chmod, chgrp, usermod, groupadd, etc. commands. How do all these things work?
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3answers
2k views

How to clear terminal after logging out?

Currently on my laptop when I log out I can still see traces of my last activities (in tty). How can I tell it (Gentoo) to clear the screen before logging out?
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4answers
336 views

Is it possible to use pendrive as key for Linux system

I want to give high security for my linux box. So i planed to use my pen drive as key for my linux box. How can i do it ?
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2answers
330 views

Why ssh-agent group ownership is not root

Trying to understand why ssh-agent has sgid bit and found this post ssh-agent has sgid I have another question, why the group ownership of ssh-agent is nobody not root? What is the reason behind it? ...
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2answers
6k views

Why does sshd requires an absolute path?

Why does sshd require an absolute path when restarting, e.g /usr/sbin/sshd rather than sshd Are there any security implications? P.S the error message: # sshd sshd re-exec requires execution with ...
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7answers
433 views

Are there additional ways to protect SSH connections besides firewall and RSA Keys?

Sometimes I don't have a static IP and need to administrate my web server remotely. I'm looking for any additional layers of protection I could add to make opening port 22 safer. Currently I have ...
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2answers
916 views

Deleting users with nologin shell

On a security audit performed on our production Linux servers , we were asked to remove nobody user if no application are using it. I checked and could see that there are no files owned by 'nobody' ...
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2answers
1k views

Preventing access to TTY when X is killed

Assume I start an X server manually from a virtual console /dev/tty1 with xinit or startx, with the line id:3:initdefault: set in /etc/inittab. The X server gets run and put on another virtual ...
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2answers
80 views

Permissions depending on how you login: ssh/su/sudo

As user I have access to a remote linux machine where I can: sudo su - other_user Among other things, this allows me to add my own public key to authorized_keys for other_user, which effectively ...
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4answers
3k views

Force Firefox to remember passwords on particular sites

Usually, when I log into a website with username and password, Firefox asks whether it should remember the login details. When I click yes, next time I visit the website, the username and password ...
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3answers
301 views

Effectivity of shred on different file systems

man shred warns that the command is not useful on file systems that don't overwrite in-place. I don't have much knowledge about the current and upcoming file systems, but I would suspect that many of ...
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1answer
879 views

SSH Public key comment separator

I've created a SSH authentication key (with ssh-keygen) in two different servers, both with a useful comment, but the public key of one server has == between the key and the comment, while the other ...
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1answer
5k views

What is hvc0? (appearing in “who” list)

I have an Ubuntu Server, and when I type who, to see who's connected, I can see that there's a user connected, and instead of being logged to a pts/x, he's connected to hvc0. Is there something to ...
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2answers
478 views

Why is 8 numbers considered a “strong” password?

Just curious as to why 8 numbers are accepted as a password in linux (CentOS if it matters) and not 8 characters on a non-dictionary word. It's 10 vs 26 per digit after all. (52 counting CaSe ...
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1answer
621 views

Can I set a bash timeout only for virtual consoles (ctrl+alt+{f1-f6})

I know that I can set a TMOUT variable to automatically end a bash session after a specified period of inactivity. However, what I want is to apply that only to my 6 built-in virtual consoles, which ...
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3answers
288 views

Are sudo and gksudo safe?

I noticed after running a sudo command in terminal or running a administrative application that uses gksudo, it won't ask again for the password for a time (something like 5 minutes). Now let's ...
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2answers
863 views

How to disable login for an user?

My Linux has many not-human users like cron, ntp, daemon, http, etc. I want to disable anybody to login as any of this users. Real people on my machine are root and me, so only root and me should be ...
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1answer
312 views

Automated ssh login with passphrase?

Logging onto a machine over ssh typically requires a password to be entered before access is granted. Alternatively, a key/certificate (without a passphrase) can be installed onto the remote machine ...
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1answer
265 views

How can I find a Ubuntu package to use with Amazon EC2?

I'm looking to set up a new server on Amazon's EC2 and I wanted to use Ubuntu 11.04 is it is fairly new but not too new. I previously used 10.10 which I think is also very stable and time-tested. My ...
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1answer
788 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 ...
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1answer
408 views

SSH tunnel with VNC?

In theory: I have a low-power consuption machine: eee pc, ok. I need to run a virtualized windows xp on it. (Because of a windows-only program..) I need to reach it from a smartphone (Android). The ...
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1answer
96 views

Why does visudo discourage other editors?

man visudo explains that visudo will not (by default) use EDITOR or VISUAL environment variables. It states that "There is no easy way to prevent a user from gaining a root shell if the editor ...
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2answers
2k views

BCRYPT - Why doesn't the Linux Distributions use it by default?

Does OpenBSD use bcrypt by default? Why doesn't every modern Linux Distribution use BCRYPT? http://codahale.com/how-to-safely-store-a-password/ https://secure.wikimedia.org/wikipedia/en/wiki/Bcrypt ...
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1answer
40 views

Find out which kernel source files were used when kernel was compiled

I am compiling the Linux kernel for my specific hardware and I only select the drivers/options which I really need. This is in contrast to a typical distribution kernel, where they compile almost ...
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1answer
2k views

Using LDAP for authentication, how can I safely disable/deactivate an account without deleting it?

We use LDAP for authentication for thousands of users. The primary tactic we have been employing to make a user unable to login, without removing their account, is to change the LDAP attribute ...
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2answers
2k views

Setting ulimit correctly for PHP on Linux

I have /etc/security/limits.conf set to the following: nobody soft nofile 409600 nobody hard nofile 1024000 phpuser soft nofile 409600 phpuser hard nofile 1024000 httpd soft nofile 409600 httpd hard ...
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3answers
264 views

Creating linux distro for use during exam

I'm thinking about creating a liveCD having some linux on it. The distro (let's call it Exam OS) is meant to be used by students during an exam and should be, at least, unpleasent to bypass. Let's ...
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3answers
673 views

Why does time/ident/daytime/comsat run after an OpenBSD 5.2 install?

I installed an OpenBSD 5.2 using "-* & +etc* & +base* & +bsd". After finished with the install, I rebooted, then netstat -at | grep LISTEN, this is what I get for output: Why does so ...
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2answers
2k views

Why is mount.cifs not installed suid by default?

I am using Gentoo, and on my machine at least mount.cifs is not installed suid root by default. In particular, this means that I can't use the user mount option with CIFS shares. I noticed that ...
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1answer
191 views

How do I know which files will be included in a linux kernel before I build it?

I am working on a project that includes building an old kernel version of linux. This is fine, but I still need to patch the kernel of all previously found security vulnerabilities based on CVEs. I ...
5
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1answer
100 views

Sterilize PDF files

I use Linux on my desktop, but I got suprised after checking random PDF files on my machines with Virustotal. One of them contained a "PDF.Exploit.CVE_2008_2992". So PDF files can have malicious ...
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1answer
669 views

Save password in bash script for multiple queries

I would like to know if there is a safe way to only be queried for a password once in a custom bash script, and then save it somehow to be used for later needs. At the end of the script it should be ...
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1answer
361 views

Secure access to remote SSH tunnel

So I wish to be able to access my Raspberry Pi (which I keep at home behind a firewall) remotely. One option is to use a static IP address, but as a poor student I don't want to fork out for one, and ...
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1answer
668 views

Ubuntu: If anyone can get a root prompt without password, isn't that compromising the gnome keyring?

I've been looking for this for quite a while now but couldn't find a satisfying answer. My scenario: I'm using encfs to encrypt a few directories in my home folder. To make it easier to access I set ...
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1answer
715 views

What are EXT4 Security Labels?

During Gentoo installation of Gnome keyring, I am told to switch on EXT4 Security Labels, which is described in the kernel documentation by: Security labels support alternative access control ...
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4answers
617 views

Allowing rename but not moving to other directory

Users can upload/delete/rename files via vsftp server and everything works well except they can also move files across directories. Is it possible to allow renaming of files but disallow moving them ...
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1answer
1k views

Which home directory should 'nobody' have?

I'm messing around with Tiger security audits on my CentOS box, ensuring the server is fit for being online, well as close as it can get anyway. I noticed a warning about the user nobody having / as ...
5
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1answer
187 views

OpenBSD and limiting login to local only like in FreeBSD's login.access(5)

I am using OpenBSD as my desktop. I don't want to login to my machine remotely, and I don't want anyone else to login remotely. In FreeBSD there is a file called login.access(5) that can be used to ...
5
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2answers
2k views

Can KWallet manage my ssh passwords?

I need a way to store some SSH passwords. Note that these are login passwords which I need to pass to ssh; key authentication is unfortunately not an option. I'd like to be able to have KWallet fill ...
5
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2answers
2k views

Hide processes from other users based on groups (under Linux)?

Is it possible to configure process hiding for certain user groups under a linux system? For example: Users from group X should not see processes owned by users from group Y in ps/top or under /proc. ...
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0answers
86 views

Does Android's implementation of SELinux's M.A.C. inhibit root apps with root privileges from accessing app data? [closed]

Starting with Android 4.4 SELinux's MAC is enforced. Does this mean that if an app somehow can get installed and exploit the kernel to get root privileges, that MAC will still prevent that app with ...
5
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1answer
552 views

gdm greeter configuration: Exclude all *except* for one specific user

I have Googled this one and tried so many combinations, with no success. I need the GDM login greeter to display one and only one username. In effect, what I need is something like this in ...
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2answers
449 views

Myth or reality: SELinux can confine the root user?

I read or heard somewhere (maybe in LinuxCBT's SELinux course; but I'm not sure) that there are online Linux servers, for which the password of the root user is also given. The Linux server is ...
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1answer
41 views

Need More Information About KDE Job Notification

I installed Debian 7.2 on a new laptop a couple of days ago, and now I'm getting a strange job notification every once in a while. It just says the following: Source: ...
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1answer
189 views

Why Nmap fragmented scan on Linux is only working from virtual environment?

OLD QUESTION AND TITLE (Look further down for the updated question): Why Nmap fragmented scan is only working on Backtrack? I spent quite a few hours today trying to capture and study some ...
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3answers
740 views

Any disk encryption that locks itself for some time after a number of failed attempts?

Is there any way to have your disk/partition/file encrypted (in Linux or as a hardware encryption; no Windows here) in such way that it locks itself for say 10 minutes after say 3 failed unlock ...
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3answers
1k views

Stracing su and ssh shows the password. Is this a security flaw or am I missing something?

I'm currently fascinated by strace so, being new to it, I decided to play around a little. As suggested by the question title, I tried both strace su and strace ssh. Both commands displayed the ...
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3answers
1k views

rsync server/daemon security

I have a NAS (Netgear Readynas NV+) at home and a linux (Arch) box at work that is always on. The linux box is already running an ssh server/daemon and the NAS is already running an rsync ...
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3answers
545 views

Securely feeding a program with a password

After understanding the problem with using a password in the command line, I need to find a way of feeding a program with a password without it being a problem (without the password being recorded ...
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3answers
4k views

What are the world writable directories by default?

In a standard Linux filesystem, which of these common directories are world-writable by default? /tmp /etc /var /proc /bin /boot /.... .... Why are they world-writable? Does that pose ...