/dev/chat

overexchange

11:46 AM

Hello Guys...

Am trying to understand the user management in Linux

avazula

Hi

What's your question?

overexchange

Am working on a Linux machine provided by my admins... Got root access for 2 weeks

Now... the non root user that I login with(say user123) takes me to /users/user123

But user123 does not exist in /etc/passwd

682

Q: A command to list all users? And how to add, delete, modify users?

I need a command to list all users in terminal. And how to add, delete, modify users from terminal. That could help in administrating your accounts easily by terminal.

@avazula Why am doing this exercise? Will let u know.. once I understand this part..

Interestingly two machines that I access with user123 has shared filesystem... that means... from my laptop, if I scp a file into /users/user123 then both machines will see the file in /users/user123

This is all new for me...

Please help me understand this..

So.. what is user123? Is it not the real user?

# cat /etc/passwd | grep user123 gives nothing

avazula

@overexchange That's weird

overexchange

hmm

Our admins are pretty smart.. because security is high priority in the sector I work for...

avazula

Why do you care to see user123?

overexchange

11:57 AM

ok

avazula

I'm not sure being root allows you to do it

I'm kinda noob* though

Let me see

overexchange

What is nood?

Sorry am not good in English...

Dictionary is not helping me... understand your English

avazula

noob. That means new/not good at it.

overexchange

oh ok

avazula

Have you tried typing cut -d: -f1 /etc/passwd | grep user123 ?

overexchange

12:00 PM

yes

same result

avazula

mmh

Have you asked this question on the forum associated with your Linux OS?

overexchange

am asking now..

avazula

If you're new to asking be careful to include all details you've told me. It'll spare you time :)

overexchange

yes

terdon

@overexchange Your system is probably using LDAP

Lightweight Directory Access Protocol

The Lightweight Directory Access Protocol (LDAP ) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network. Directory services play an important role in developing intranet and Internet applications by allowing the sharing of information about users, systems, networks, services, and applications throughout the network. As examples, directory services may provide any organized set of records, often with a hierarchical structure, such as a corporate email directory. Similarly...

Your user isn't actually defined as a local user to the machine you are logging into, that's why it's not in passwd

overexchange

12:12 PM

ok

 # df -h /users/user123
    Filesystem                                           Size  Used Avail Use% Mounted on
    catonddff.abc.xyz.com:/vol/DDD0_ABCUSERS/prod/user123  1.6T  1.3T  301G  82% /users/user123

@terdon Do you understand something from this?

terdon

@overexchange Only that user123's home directory is mounted from the remote server catonddff.abc.xyz.com

avazula

@terdon which explains why they can't see it in /etc/passwd as root, right?

overexchange

you mean... 1.6T space is mounted from catonddff.abc.xyz.com to my unix machine

terdon

But I don't really know how LDAP works, I've used systems using it, but I have never set it up myself. The answer to your main question, "why is my user not in /etc/passwd?", however, is "because your user is set up via LDAP and isn't a local user"

overexchange

Am able to sudo su - with user123

How do I understand this?

terdon

12:14 PM

@avazula yep. And no need for root, simply grep user123 /etc/passwd would have been enough if the user were there

@overexchange yes

@overexchange What don't you understand?

I mean, what is confusing you?

avazula

@terdon makes sense to me

overexchange

Is user123 existing on linux machine?

terdon

The LDAP user acts like a regular user for the machine. It just doesn't have an entry in /etc/passwd.

@overexchange Kinda :) It is a network user, not defined on the local machine, but the local machine validates users through LDAP somehow. I really don't know the details.

overexchange

ok

Now.. my next question...

I installed an application using root...

terdon

the main point is that i) the user is not defined on the local machine but is defined via LDAP and ii) the local machine uses LDAP to authenticate the user and, once authenticated, the user can act like a normal, local user. So you can use sudo (not sudo su -, please).

70

Q: Is there ever a good reason to run sudo su?

To launch a root shell on machines where the root account is disabled, you can run one of: sudo -i : run an interactive login shell (reads /root/.bashrc and /root/.profile) sudo -s : run a non-login interactive shell (reads /root/.bashrc) In the Ubuntu world, I very often see sudo su suggeste...

shell sudo environment-variables su

overexchange

12:18 PM

For security reasons... I cannot take root privilege to run/administrate that application..

So Do I need to create a local non root user?

terdon

@overexchange You already have one: user123

Why do you need a local one?

overexchange

ok

Now.. sudo su - privilege will be lost for user123 in 2 weeks..

terdon

sudo privilege, yes

overexchange

So.. I need to create a non root user that does not have sudo su - privilege...

terdon

why?

Just don't use sudo.

overexchange

12:21 PM

I mean the new user should not get root provilege

terdon

And never use sudo su, it's ugly and pointless. Use sudo -i instead.

@overexchange Again, why?

Why make a new user at all? What's wrong with the user you already have?

overexchange

ok

am a contractor and I will leave in 3 months...

So my user name(user123) will be purged in 3 months automatically

terdon

OK

But you still haven't explained why you need a new user.

overexchange

ok

terdon

If someone else needs to use the tool you installed, they can use it with their user.

overexchange

12:24 PM

My mgr asks me to create a syslog user and have the application able to run as that user.... I installed Syslog-NG as root

ls /users only has user123

terdon

@overexchange I don't know what a syslog user is. if you just mean a user whose only reason to exist is to run this Syslog-NG thing, then just create a new user. However, if you do this on the local machine, then the user will only exist on the local machine.

overexchange

I mean just a user.... whose only reason to exist is to run this Syslog-NG thing

terdon

You should talk to your sysadmin if you need to create a new LDAP user.

@overexchange Great, so create one.

overexchange

ok

But how to know/inform the privilege levels of any existing LDAP user? For example user123

To inform sysadmin..

What is the command to know the privilege levels of user123?

terdon

@overexchange this is why you really should post questions instead of asking in chat. That way you can actually explain the entire situation. Why do you need to inform the sysadmin? Why do you need to know the privilege levels of user123? What do you even mean by "privilege levels"? Why is user123 relevant if it's going to be deleted in 2 weeks?

overexchange

12:31 PM

user123 will not be deleted in 2 weeks... it will be deleted after 3 months.. which is not the concern..

user123 as sudoer will be removed after 2 weeks

Idea to create a syslog user is to then sudo to the syslog user to maintain the application.

terdon

ok

overexchange

and this syslog user will be forever as sudoer..

Every body will login with this username..

Can that be a LDAP user or local user is a different question..

sysadmin will decide it...

Most probably it should be local user...

because this user belongs to an application but not to any employee...

overexchange

1:53 PM

@terdon Do i need to ask such questions in superuser or unix forum?

Because I asked in unix forum..

terdon

No, Unix is fine

overexchange

ok

0

Q: Changing group ownership of files - User management

Installed an application as root owner but not as non-root. why? Because we had to install this application in custom location(/app) So, after installing an application(Syslog-NG), below are the files with current ownership: # ls -l /app/syslog-ng/etc/syslog-ng.conf -rw-r--r-- 1 root root 938 A...

linux rhel users not-root-user syslog-ng

terdon

It's just better to post a question than asking in chat

@overexchange Cool, thanks!

overexchange

After talking to you... I got clarity on what to ask?

There are levels in subject matter expertise...

1) Unconciously Incompetent 2) Conciously Incompetent 3) Conciously competent, 4) Unconciously Competent

@terdon My guess is I moved from 1 to 2 after talking to u

terdon

heh :)

overexchange

1:59 PM

hahaha

I got these MBA jargon from Agile SCRUM training... Can you imagine? Otherwise am very bad in English...

Some idiot who was not good technically... was my Agile coach in previous company I work for

BTW... every Computer science student should have these Linux skills..

Kusalananda

2:15 PM

@overexchange That's an iterative process; one usually move through all four stages many times on any given topic, each time on a deeper level.

overexchange

@Kusalananda Hai how r u man?

Last time we talked I was in previous to previous company

I have change two employers after our last chat..

I did not get u... Iterative process? Are you talking about Agile SCRUM?

Aaah i got u..

If a technician is Iterative then that means... he is making mistake to learn first principles of his domain...

It should not be iterative..

2,3,4 can be iterative...

Currently ...

ls -l /app/syslog-ng/etc/syslog-ng.conf
-rw-r--r-- 1 root root 938 Aug 20 12:43 /app/syslog-ng/etc/syslog-ng.conf

After running this command sudo chgrp foo /app/syslog-ng/etc/syslog-ng.conf

file should have permissions like..

ls -l /app/syslog-ng/etc/syslog-ng.conf
-rw-rw-r-- 1 root foo 938 Aug 20 12:43 /app/syslog-ng/etc/syslog-ng.conf

Is that correct?

Manuel Rodriguez

2:31 PM

@Kusalananda That is right, rule evaluation is a concrete example. The expert system checks all the rules and if no one is firing anymore the reasoning process stops.

Kusalananda

@overexchange Hmm... Why did the permissions change?

overexchange

Forgot to copy paste: sudo chmod 664 /app/syslog-ng/etc/syslog-ng.conf

But I would be running these commands as root.. I would not need to sudo these commands.. Is that correct?

Kusalananda

@overexchange If you are running the commands as root, you will not need sudo, that is correct.

overexchange

ok

Why every user is able to run this binary?

# ls -l /app/syslog-ng/sbin/syslog-ng
-rwxr-xr-x 1 root root 39768 Aug 20 12:43 /app/syslog-ng/sbin/syslog-ng

r-x with group name as root

So... how come a new local user(non root) created will be able to execute?

without chgrp command

Kusalananda

@overexchange Because the user, the group, and everyone else has both r and x permissions on the binary.

Prabhjot Singh

2:38 PM

Hi everyone

overexchange

ok

So this new user will be part of everyone else in the list of users.. Is that correct?

Prabhjot Singh

I am getting segmentation fault(core dumped).

Kusalananda

@overexchange If you removed the r and x permissions for "other", with chmod o-rx filename, then only the owner and group could execute it.

@PrabhjotSingh Then you've done something wrong.

overexchange

hahaha

Kusalananda

@overexchange That is correct.

overexchange

2:40 PM

something wrong..

hahaha

Prabhjot Singh

This happens in my Fedora machine. But in windows this runs perfectly

Kusalananda

@PrabhjotSingh Is it a C program?

overexchange

Ya So... Fedora has dome something wrong..

What is the stack trace?

Prabhjot Singh

@Kusalananda yes

overexchange

SIGSEGV

Kusalananda

2:42 PM

@PrabhjotSingh Different compilers (even different versions of the same compiler) may generate code that handles buffer overruns differently, but getting a segmentation fault is generally a sign of a buffer overrun. An array is not large enough to hold the data, or you're stepping off the end of an array.

Manuel Rodriguez

@overexchange I've thought about the OP bit deeper and found a first answer to the problem of group ownership. The first step is to model the UNIX permissions in an ontology. In the second step the formal model can used by a PDDL like planner to generate an attack plan. The third step is to execute the attack plan against the target. So, how does look your model?

Kusalananda

The fact that Windows manages to run the code just means that the space allocated for your array is not followed by anything essential, and that the runtime system doesn't catch you walking off the end of it (which it should do IMHO).

overexchange

or a C pointer pointing to some weird location..

Kusalananda

@overexchange Well, the location after the end of an array is a weird location.

overexchange

Pointer pointing to 0x100(say kernel space) is one possibility.... crossing array boundary into another process space is another possibility... Same reason....

Kusalananda

2:47 PM

@overexchange I believe that that should cause a bus error, since that memory should be protected and not available to a user space process. But I'm not sure.

overexchange

@PrabhjotSingh As problem is in linux... have source code in hand.. take core dump and play with gdb

Just google gdb coredump

bt should give the reason

I dont remember the steps now.. I did this in 2008-2009

@Kusalananda Now... for an LDAP user to modify this file...

ls -l /app/syslog-ng/etc/syslog-ng.conf
-rw-rw-r-- 1 root foo 938 Aug 20 12:43 /app/syslog-ng/etc/syslog-ng.conf

What are the steps required?

In this answer he did not mention.. how to add a user in that group?

adduser user1

How to add user1 into foo?

@Kusalananda Does the answer look incomplete?

Kusalananda

3:35 PM

@overexchange It looks like an ok answer to me, but it does not address the fact that you have users in an LDAP database. Unfortunately I have zero experience with LDAP.

overexchange

4:38 PM

@Kusalananda An employe will first login with his own LDAP username to Linux machine and sudo to this local user to work with app.. I did not get u...

Rui F Ribeiro

8:46 PM

te

Tempted to close this as a duplicate of Kalihttps://unix.stackexchange.com/questions/463950/ubuntu-not-replying-to-arp-r‌equests Script kiddies use exploits/dark utils and then come asking incomplete questions wondering why things change behaviour.

2

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