Overview
whois is a protocol and client program used to query registration data for internet domain names and IP addresses. This information helps identify domain owners, registrars, and contact details.
Key Information Provided
The following are the typical pieces of information you can obtain from a whois query:
- Domain owner information (may be restricted due to privacy regulations)
- Registrar information
- Domain registration and expiration dates
- Domain status (e.g., clientTransferProhibited)
- Nameserver information
- Administrative and technical contact information (may be restricted)
Key Options
The whois command allows you to control the lookup process through various options.
Lookup Control
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Description:
`whois` Executes the command.
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Usage Examples
Here are some common usage examples for the whois command.
Basic Domain Information Lookup
whois example.comQueries WHOIS information for the specified domain name.
IP Address Information Lookup
whois 8.8.8.8Queries WHOIS information for the specified IP address. This typically returns information from the RIR (Regional Internet Registry) that allocated the IP block.
Query Using a Specific WHOIS Server
whois -h whois.nic.or.kr example.co.krTypically, .kr domains can be queried through the WHOIS server of the Korea Internet & Security Agency (KISA).
Query Without Header Information
whois -H example.comOutputs only the raw WHOIS data, excluding header information such as legal disclaimers.
Installation
The whois command may not be included by default in most Linux distributions. You can install it using the following commands.
Debian/Ubuntu
sudo apt update && sudo apt install whoisInstalls the whois package using the APT package manager.
CentOS/RHEL/Fedora
sudo dnf install whoisInstalls the whois package using the DNF (or yum) package manager.
Tips & Precautions
Useful tips and points to be aware of when using whois.
Privacy (GDPR, etc.)
Due to privacy regulations like GDPR (General Data Protection Regulation), WHOIS information for many domains may be anonymized or displayed with limited details. Especially for individual registrants, contact information is often masked. This can hinder legitimate inquiries.
Rate Limiting
Some WHOIS servers may limit the number of queries to prevent excessive usage. Attempting too many queries in a short period can result in a temporary ban, so exercise caution when using automated scripts.
Checking RIR Information for IP Address Lookups
WHOIS lookups for IP addresses return information from the RIR (Regional Internet Registry) that allocated the IP address. For example, IPs in the Asia-Pacific region will show information from APNIC, and those in North America from ARIN. This allows you to check the owner and allocation details of IP blocks.
Various WHOIS Servers
The WHOIS server to query may vary depending on the domain extension (.com, .org, .kr, etc.) or the allocation region of the IP address. While the whois command attempts to handle this automatically, you may sometimes need to explicitly specify a server using the -h option.