Recently, I was tasked with troubleshooting a web server running on a Debian system. The server had been throwing an error whenever certain requests were made, stating “Invalid Argument”. After researching the error, I determined that the best solution to resolving the issue was to use the dig utility.
Dig, also known as Domain Information Groper, is a command line utility that can be used to find out information about domain name systems (DNS). Many times, when troubleshooting DNS issues, the information it provides can be invaluable. In this case, the Invalid Argument error was being thrown as a result of a DNS issue, and, using the dig utility, I was able to track down the root cause and get the server up and running again.
To begin, I accessed the server via SSH (Secure Shell) as the root user. I then entered the command dig -t A www.my-domain.com, which essentially instructs the dig utility to query a DNS server for the A record (the address of the server hosting my domain). This command returned the following response:
;; Truncated, retrying in TCP mode. ;; connection timed out; no servers could be reached
This indicated that the DNS server was not working properly. To investigate further, I ran the command dig @8.8.8.8 -t A www.my-domain.com. I used the “@” symbol and a Google DNS server’s IP address (in this case, 8.8.8.8) to directly query a specific DNS server instead of relying on the server configured on the Debian system. This command returned the A record, confirming that the DNS server was not the issue.
Next, I checked to see if there were any DNS related errors in the system’s log files. To do this, I used the command tail -f /var/log/syslog. This command allowed me to view any new errors as they occurred. Sure enough, I found several errors related to the DNS server.
The root cause of the issue was a misconfiguration of the DNS server on the Debian system. To fix this, I edited the /etc/resolv.conf file to update the IP address of the DNS server. I then restarted the DNS server, and the issue was resolved.
In summary, the Invalid Argument error on the Debian system was due to a misconfiguration of the DNS server. The dig utility was invaluable in tracking down the source of the issue, and by editing the /etc/resolv.conf file and restarting the DNS server, I was able to resolve the problem.
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