Red Hat Enterprise Linux Diagnostics and Troubleshooting

Troubleshoot and resolve the program application issue.

1. Log in to servera and switch to the root user.

   [student@workstation ~]$ ssh student@servera
   ...output omitted...
   [student@servera ~]$ sudo -i
   [sudo] password for student: student
   [root@servera ~]#

2. Attempt to run the program command, and view any messages.

   The runtime linker cannot open the libreadline.so.7 library.

   [root@servera ~]# program
   program: error while loading shared libraries: libreadline.so.7: cannot open shared object file: No such file or directory

3. Discover whether any other shared libraries cannot be resolved.

   No other libraries are missing.

   [root@servera ~]# which program
   /usr/bin/program
   [root@servera ~]# ldd /usr/bin/program
   	linux-vdso.so.1 (0x00007ffc55d92000)
   	libreadline.so.7 => not found
   	libc.so.6 => /lib64/libc.so.6 (0x00007f193603f000)
   	/lib64/ld-linux-x86-64.so.2 (0x00007f1936404000)

4. Identify the package that provides the missing shared library.

   [root@servera ~]# yum provides libreadline.so.7
   Last metadata expiration check: 2:05:19 ago on Fri 12 Nov 2021 02:41:41 PM EST.
   readline-7.0-10.el8.i686 : A library for editing typed command lines
   Repo        : rhel-8.4-for-x86_64-baseos-rpms
   Matched from:
   Provide    : libreadline.so.7

5. Install the required packages.

   The package is present, but the library that it provides is missing.

   [root@servera ~]# yum install readline
   Last metadata expiration check: 2:06:19 ago on Fri 12 Nov 2021 02:41:41 PM EST.
   Package readline-7.0-10.el8.x86_64 is already installed.
   Dependencies resolved.
   Nothing to do.
   Complete!

6. Verify the package's files.

   The library file is missing.

   [root@servera ~]# rpm -V readline
   missing     /usr/lib64/libreadline.so.7

7. Reinstall the package to restore the missing file.

   [root@servera ~]# yum reinstall readline
   ...output omitted...
   Reinstalled:
     readline-7.0-10.el8.x86_64
   
   Complete!

8. Attempt to run the program command, and view any messages. When prompted, enter a string of characters.

   The application is starting, but presents a new error.

   [root@servera ~]# program
   Enter value: anystring
   Error: application failed to run!

Troubleshoot and resolve the additional program application issue.

1. View the application's system calls.

   The strace output will pause when it reaches the string input prompt. Press Enter to view the full output.

   The application tries to connect to port 80 on the local system, but the connection is refused.

   [root@servera ~]# strace program
   execve("/usr/bin/program", ["program"], 0x7ffcb6e91dd0 /* 25 vars */) = 0
   ...output omitted...
   connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ECONNREFUSED (Connection refused)
   write(1, "Error: application failed to run"..., 34Error: application failed to run!
   ) = 34
   exit_group(1)                           = ?
    exited with 1

2. The application relies on a local web service to be running. Verify whether one is installed.

   [root@servera ~]# systemctl status httpd
   Unit httpd.service could not be found.

3. Install and start a web server to listen on port 80.

   [root@servera ~]# yum install httpd
   ...output omitted...
   [root@servera ~]# systemctl start httpd

4. Attempt to run the program command, and view any messages.

   The "Success!" output indicates that the program application is functioning properly.

   [root@servera ~]# program
   Enter value: anystring
   Success!

5. Return to workstation as the student user.

   [root@servera ~]# exit
   [student@servera ~]$ exit
   [student@workstation ~]$