Red Hat System Administration II

[student@workstation ~]$ ssh student@serverb
...output omitted...

[student@serverb ~]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/student/.ssh/id_rsa): Enter
Created directory '/home/student/.ssh'.
Enter passphrase (empty for no passphrase): Enter
Enter same passphrase again: Enter
Your identification has been saved in /home/student/.ssh/id_rsa.
Your public key has been saved in /home/student/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:1TPZ4TXYwiGWfExUGtRTHgfKQbF9hVuLa+VmH4vgkFY student@serverb.lab.example.com
The key's randomart image is:
+---[RSA 2048]----+
|          .+@BO**|
|          .=.#+B*|
|          . X.*o=|
|         . E +.+ |
|        S o   +  |
|         + . o = |
|        . o o + +|
|           . . ..|
|                 |
+----[SHA256]-----+

Use the ssh-copy-id command to transfer the public key of the SSH key pair of student on serverb to student on servera. Use student as the password of the student user, if prompted.

[student@serverb ~]$ ssh-copy-id student@servera
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/student/.ssh/id_rsa.pub"
The authenticity of host 'servera (172.25.250.10)' can't be established.
ECDSA key fingerprint is SHA256:g/fIMtVzDWTbTi1l0OwC30sL6cHmro9Tf563NxmeyyE.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
student@servera's password: student

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'student@servera'"
and check to make sure that only the key(s) you wanted were added.

Use the ssh command to verify that the student user can log in to servera from serverb without entering a password.

[student@serverb ~]$ ssh student@servera
...output omitted...
[student@servera ~]$ 

Edit /etc/sysconfig/selinux to set the value of the parameter SELINUX to permissive. You can use the sudo vi /etc/sysconfig/selinux command to edit the configuration file as the superuser. Use the password student, if prompted.

...output omitted...
#SELINUX=enforcing
SELINUX=permissive
...output omitted...

Use the sudo systemctl reboot command to reboot the system as the superuser.

[student@servera ~]$ sudo systemctl reboot
Connection to servera closed by remote host.
Connection to servera closed.
[student@serverb ~]$ 

On serverb, use the sudo -i command to switch to the root user account.

[student@serverb ~]$ sudo -i
[sudo] password for student: student
[root@serverb ~]# 

Install the autofs package.

[root@serverb ~]# yum install autofs
...output omitted...
Is this ok [y/N]: y
...output omitted...
Installed:
  autofs-1:5.1.4-29.el8.x86_64

Complete!

Create the autofs master map file called /etc/auto.master.d/production5.autofs with the following content.

/- /etc/auto.production5

Retrieve the details of the production5 user to get the home directory path.

[root@serverb ~]# getent passwd production5
production5:x:5001:5001::/localhome/production5:/bin/bash

Create the /etc/auto.production5 file with the following content.

/localhome/production5 -rw servera.lab.example.com:/home-directories/production5

Restart the autofs service.

[root@serverb ~]# systemctl restart autofs

From workstation, open an SSH session to servera as student.

[student@workstation ~]$ ssh student@servera
...output omitted...
[student@servera ~]$ 

Switch to the production5 user using the password redhat.

[student@servera ~]$ su - production5
Password: redhat
[production5@servera ~]$ 

Use the ssh-keygen command to generate the SSH keys as production5.

[production5@servera ~]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/production5/.ssh/id_rsa): Enter
Created directory '/home/production5/.ssh'.
Enter passphrase (empty for no passphrase): Enter
Enter same passphrase again: Enter
Your identification has been saved in /home/production5/.ssh/id_rsa.
Your public key has been saved in /home/production5/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:zmin1nmCt4H8LA+4FPimtdg81nl7ATbInUFW3HSPxk4 production5@servera.lab.example.com
The key's randomart image is:
+---[RSA 2048]----+
|       .oo.o. .  |
|       .. . .o o |
|     . o o    E .|
|   .  o *    +   |
|  . .  .So    .  |
|   . + =  .      |
|    *.*+=. .     |
|   Oo+***.o      |
|  o.=o.=**       |
+----[SHA256]-----+

Use the ssh-copy-id command to transfer the public key of the SSH key pair of production5 on servera to production5 on serverb. Use redhat as the password of the production5 user, if prompted.

[production5@servera ~]$ ssh-copy-id production5@serverb
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/production5/.ssh/id_rsa.pub"
The authenticity of host 'serverb (172.25.250.11)' can't be established.
ECDSA key fingerprint is SHA256:ciCkaRWF4g6eR9nSdPxQ7KL8czpViXal6BousK544TY.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
production5@serverb's password: redhat

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'production5@serverb'"
and check to make sure that only the key(s) you wanted were added.

Use the SSH public key-based authentication instead of password-based authentication to log in to serverb as production5. This command should fail.

[production5@servera ~]$ ssh -o pubkeyauthentication=yes \
-o passwordauthentication=no production5@serverb
production5@serverb: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).

On serverb as root, set the use_nfs_home_dirs SELinux Boolean to true.

[root@serverb ~]# setsebool -P use_nfs_home_dirs true

Use the SSH public key-based authentication instead of password-based authentication to log in to serverb as production5. This command should succeed.

[production5@servera ~]$ ssh -o pubkeyauthentication=yes \
-o passwordauthentication=no production5@serverb
...output omitted...
[production5@serverb ~]$ 

Use the firewall-cmd command to add the IPv4 address of servera to the firewalld zone called block.

[root@serverb ~]# firewall-cmd --add-source=172.25.250.10/32 \
--zone=block --permanent
success

Use the firewall-cmd --reload command to reload the changes in the firewall settings.

[root@serverb ~]# firewall-cmd --reload
success

Use the systemctl command to restart the httpd service. This command fails to restart the service.

[root@serverb ~]# systemctl restart httpd.service
Job for httpd.service failed because the control process exited with error code.
See "systemctl status httpd.service" and "journalctl -xe" for details.

Use the systemctl status command to investigate the reason for the failure of the httpd service.

[root@serverb ~]# systemctl status httpd.service
● httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2019-04-15 06:42:41 EDT; 5min ago
     Docs: man:httpd.service(8)
  Process: 27313 ExecStart=/usr/sbin/httpd $OPTIONS -DFOREGROUND (code=exited, status=1/FAILURE)
 Main PID: 27313 (code=exited, status=1/FAILURE)
   Status: "Reading configuration..."

Apr 15 06:42:41 serverb.lab.example.com systemd[1]: Starting The Apache HTTP Server...
Apr 15 06:42:41 serverb.lab.example.com httpd[27313]: (13)Permission denied: AH00072: make_sock: could not bind to address [::]:30080
Apr 15 06:42:41 serverb.lab.example.com httpd[27313]: (13)Permission denied: AH00072: make_sock: could not bind to address 0.0.0.0:30080
Apr 15 06:42:41 serverb.lab.example.com httpd[27313]: no listening sockets available, shutting down
Apr 15 06:42:41 serverb.lab.example.com httpd[27313]: AH00015: Unable to open logs
Apr 15 06:42:41 serverb.lab.example.com systemd[1]: httpd.service: Main process exited, code=exited, status=1/FAILURE
Apr 15 06:42:41 serverb.lab.example.com systemd[1]: httpd.service: Failed with result 'exit-code'.
Apr 15 06:42:41 serverb.lab.example.com systemd[1]: Failed to start The Apache HTTP Server.

Notice the permission error in the preceding output, which signifies that the httpd daemon failed to bind to port 30080/TCP. The SELinux policy can be a potential restriction for an application to bind to a port. Press q to quit the preceding systemctl command.

Use the sealert command to determine if an SELinux policy is preventing httpd from binding to port 30080/TCP.

[root@serverb ~]# sealert -a /var/log/audit/audit.log
100% done
found 1 alerts in /var/log/audit/audit.log
--------------------------------------------------------------------------------

SELinux is preventing /usr/sbin/httpd from name_bind access on the tcp_socket port 30080.

*****  Plugin bind_ports (92.2 confidence) suggests   ************************

If you want to allow /usr/sbin/httpd to bind to network port 30080
Then you need to modify the port type.
Do
# semanage port -a -t PORT_TYPE -p tcp 30080
    where PORT_TYPE is one of the following: http_cache_port_t, http_port_t, jboss_management_port_t, jboss_messaging_port_t, ntop_port_t, puppet_port_t.
...output omitted...

The preceding log message reveals that the port 30080/TCP does not have the appropriate SELinux context http_port_t, causing SELinux to prevent httpd to bind to this port. The log message also produces the syntax of the semanage port command so that you can easily fix the issue.

Use the semanage port command to set the appropriate SELinux context on the port 30080/TCP for httpd to bind to it.

[root@serverb ~]# semanage port -a -t http_port_t -p tcp 30080

Use the systemctl command to restart httpd. This command should successfully restart the service.

[root@serverb ~]# systemctl restart httpd

Add the port 30080/TCP to the default firewalld zone called public.

[root@serverb ~]# firewall-cmd --add-port=30080/tcp --permanent
success
[root@serverb ~]# firewall-cmd --reload
success

Exit the root user's shell.

[root@serverb ~]# exit
logout

Log off from serverb.

[student@serverb ~]$ exit
logout
Connection to serverb closed.