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Question

I can't change a directory's owner even if I'm root.

I want to build a NAS by using raspberry 3B+.

1. So I have created a user named dorm.
2. Then I changed sshd_file in order to restrict SFTP users(dorm) to only visit his home directories

3. Now the user(dorm) doesn't have the write permission. So After I google it,I should mkdir a 777 directory at /home/dorm/ .So I made it by root.
4. Then I wanna change its owner by chown -R dorm:dorm /home/dorm/Documents. I failed.

Answer 1

Maybe its best to remove the user and try again, this is what I did to make it work.

1. log into newly setup raspberry pi as pi user, only default logins exist.

pi@raspberrypi:~ $ whoami
pi
pi@raspberrypi:~ $ lslogins -u
 UID USER PROC PWD-LOCK PWD-DENY LAST-LOGIN GECOS
   0 root   84                              root
1000 pi      5                        15:31 ,,,

2. add new user dorm

$ sudo adduser dorm
Adding user `dorm' ...
Adding new group `dorm' (1001) ...
Adding new user `dorm' (1001) with group `dorm' ...
Creating home directory `/home/dorm' ...
Copying files from `/etc/skel' ...
New password:
Retype new password:
passwd: password updated successfully
Changing the user information for dorm
Enter the new value, or press ENTER for the default
    Full Name []:
    Room Number []:
    Work Phone []:
    Home Phone []:
    Other []:
Is the information correct? [Y/n] y

pi@raspberrypi:~ $ lslogins -u
 UID USER PROC PWD-LOCK PWD-DENY LAST-LOGIN GECOS
   0 root   87                              root
1000 pi      5                        15:31 ,,,
1001 dorm    0                              ,,,

3. make a backup and edit your sshd_config file,

pi@raspberrypi:~ $ sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config-bak
pi@raspberrypi:~ $ sudo vim /etc/ssh/sshd_config
pi@raspberrypi:~ $ diff /etc/ssh/sshd_config /etc/ssh/sshd_config-bak
122,128d121
<
< Match User dorm
<     X11Forwarding no
<     AllowTcpForwarding no
<     PermitTTY no
<     ForceCommand internal-sftp
<     ChrootDirectory /home/dorm

4. restart ssh service with sudo service sshd restart
5. change the ownership of the dorm home directory to root.

$ sudo chown root:root /home/dorm
$ sudo chmod 755 /home/dorm

6. from the dorm user's directory use sudo as the pi user to create the Documents folder and give ownership to the dorm user

pi@raspberrypi:/home/dorm $ ls
pi@raspberrypi:/home/dorm $ mkdir Documents
mkdir: cannot create directory ‘Documents’: Permission denied
pi@raspberrypi:/home/dorm $ sudo mkdir Documents
pi@raspberrypi:/home/dorm $ ls -l
total 4
drwxr-xr-x 2 root root 4096 Feb  8 18:15 Documents
pi@raspberrypi:/home/dorm $ sudo chown -R dorm:dorm Documents
pi@raspberrypi:/home/dorm $ ls -l
total 4
drwxr-xr-x 2 dorm dorm 4096 Feb  8 18:15 Documents

7. test the connection etc. using your IP address from your host computer (ssh should reply No route to host )

$ sftp dorm@<IP>
dorm@<IP>'s password:
Connected to dorm@<IP>.
sftp>

• you can see the created Documents folder and the user number that owns it (dorm's number)

sftp> ls -ltr
drwxr-xr-x    2 1001     1001         4096 Feb  8 18:15 Documents

• you can't move out of the base directory

sftp> pwd
Remote working directory: /
sftp> cd ..
sftp> pwd
Remote working directory: /

• you can't put files in the base directory as dorm doesn't have permissions. (file path will need to be altered for your system)

sftp> put /Users/<USER>/tmp
Uploading /Users/<USER>/tmp to /tmp
remote open("/tmp"): Permission denied

• if you move into Documents then you can then upload files

sftp> cd Documents
sftp> put /Users/<USER>/tmp
Uploading /Users/<USER>/tmp to /Documents/tmp
/Users/<USER>/tmp                                                                       100%    0     0.0KB/s   00:00