How to Check Certificate Expiry and HTTPS Chain via OpenSSL
We separately verify the local certificate and what the server actually serves: validity period, hostname, and chain trust require distinct checks.
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3 minViews2
GENERAL IT · JOURNAL
Tips and solutions
Practical tips and verified solutions for Linux, servers and websites.
How to Check the Installed Package Version and Update Source in Ubuntu
We verify the package using dpkg-query and apt-cache policy, distinguishing between the installed version, the candidate for update, and the actual source of the running process.
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3 minViews0
How to Find Which Process Is Listening on a Port in Linux
Check TCP and UDP via ss, analyze the binding address, and distinguish a local listening socket from service availability from the internet.
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3 minViews1
File Deleted, But Space Not Freed: Diagnostics with lsof
How to find deleted files still held open by processes and gather data to safely free space without accidentally stopping the service.
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3 minViews1
Disk is lagging: how to read iostat without universal thresholds
We examine latency, queue depth, and I/O operations, accounting for SSDs, virtual disks, and the difference between the first report and subsequent intervals.
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3 minViews0
How to Check MySQL Connectivity Without Confusing Availability with Permissions
Separate server operation, connection, authentication, and query execution: why a successful mysqladmin ping does not confirm application access.
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3 minViews3
How to Verify File Integrity Using SHA-256
We compare the checksum of a downloaded archive against a trusted value and explain what this verification proves and what it does not confirm.
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3 minViews1
Permission Denied: How to Find the Problem in the Path and Access Rights
Use namei and stat to check the entire file path, owner, and access mode before changing the site directory permissions.
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3 minViews2
Incorrect Server Time: Checking Clocks and Synchronization
How to use timedatectl to distinguish between a time zone error and clock desynchronization, and gather data before manually adjusting the time.
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3 minViews2
How to Measure Website Response Time with curl: Codes, Redirects, and Timing
A quick HTTP check with a timeout: distinguish connection errors from server responses and do not treat cumulative timings as independent stages.
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3 minViews1
Why dig and the app see different addresses: checking resolvectl
How to view DNS servers and name resolution rules in a systemd-resolved system, especially with VPNs and multiple network interfaces.
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3 minViews2
How to Check a DNS Record with dig and Interpret the Response Correctly
We analyze the record type, response server, status, and TTL: why empty or brief output does not equal a missing domain and when DNS comparison is useful.
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3 minViews1
How to Check Server IP Addresses and Routes Without Changing the Network
Quick diagnostics with ip: interfaces, addresses, and the selected route to the recipient. Helps gather facts without risking loss of remote access.
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3 minViews3
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