Can you switch your terminal user as any user defined in /etc/passwd?

Minsky

5/31/23, 1:13 PM

Context

This is very newbie question but I dont fully grasp unix users yet.

If I cat /etc/passwd there are different users:

me:x:1000:1000:me,,,:/home/me:/bin/bash
systemd-coredump:x:999:999:systemd Core Dumper:/:/usr/sbin/nologin
sddm:x:127:134:Simple Desktop Display Manager:/var/lib/sddm:/bin/false
mongodb:x:128:65534::/home/mongodb:/usr/sbin/nologin
sshd:x:129:65534::/run/sshd:/usr/sbin/nologin
tftp:x:130:138:tftp daemon,,,:/srv/tftp:/usr/sbin/nologin
_rpc:x:131:65534::/run/rpcbind:/usr/sbin/nologin

most of them are no login users (so we would say you can't log in unless it is a /bash user), but if I try this command:

su - mongodb

it prompts me for a password. Problem is I don't know the password in this case.

Question

but does this mean I could switch to this user in the terminal and maybe run the process as systemd-service would do?
so we would say you can't log in unless it is a /bash user?

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server

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Score:3

Ubuntu

AtomiX84

5/31/23, 1:34 PM

short answer:

If you are the super user (id=0) or commonly known as root, you cannot login in to it if shell is set to /usr/sbin/nologin or /usr/bin/false

as per the manpage description of nologin:

   **DESCRIPTION**
   nologin displays a message that an account is not available and
   exits non-zero. It is intended as a replacement shell field to
   deny login access to an account.

   If the file /etc/nologin.txt exists, nologin displays its
   contents to the user instead of the default message.

   The exit status returned by nologin is always 1.

but (always if you are root or can sudo commands) you can execute a bash as per one user which is noloign user, to impersonate him for troubleshooting

sudo:

sudo -u mongodb /bin/bash

root:

su -s /bin/bash mongodb

Those above command does not execute a login, but just execute a bash with the user permission, in this case as mongodb user.

NOTE: normally thos user are passwordless, that mean even the su - process ask you for a password that will never match with nothing also empty password.

0 + 0

AtomiX84

5/31/23, 2:36 PM

yes @steeldriver, my bad! I correct it

Minsky

5/31/23, 10:34 PM

cant thank enough

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Can you switch your terminal user as any user defined in /etc/passwd?

TH: คุณสามารถเปลี่ยนผู้ใช้เทอร์มินัลเป็นผู้ใช้ที่กำหนดไว้ใน /etc/passwd ได้หรือไม่

RO: Puteți schimba utilizatorul terminalului ca orice utilizator definit în /etc/passwd?

RU: Можете ли вы сменить пользователя терминала на любого пользователя, определенного в /etc/passwd?

VI: Bạn có thể chuyển đổi người dùng đầu cuối của mình thành bất kỳ người dùng nào được xác định trong/etc/passwd không?

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