Linux.

Linux

zstd Frame Integrity Does Not Verify Your Restored Files

A successful zstd integrity test answers one narrow question: can the compressed frame be decoded without an error? It does not prove…

Aug 15, 202614 min read

DevOps

cloud-init Uses Instance ID to Decide User Data Replay

Changing user-data bytes is not a new-instance event. By default, cloud-init decides whether per-instance modules may run from instance identity and cached…

Aug 13, 202616 min read

Database

SQLite’s Online Backup API Captures What cp Misses in WAL Mode

Both SQLite files in the reproduced lab returned quick_check=ok. Only one contained all four committed rows. The raw copy of live.db held…

Aug 13, 202614 min read

Linux

Test SMTP STARTTLS Certificate Trust and Hostname

An SMTP server can advertise STARTTLS, complete a TLS handshake, and still present an identity that a careful client must reject. Encryption…

Aug 12, 202615 min read

Linux

A Restic Restore Is Not Finished Until the Data Matches

Restic can restore bytes correctly and still return the wrong recovery point. latest is a selector, not a business decision: a shared…

Aug 10, 202614 min read

Linux

Linux Unattended Upgrades: Patch Automatically, Reboot Deliberately

unattended-upgrades can install eligible APT updates without waiting for an administrator. It cannot decide whether a service may restart during business hours,…

Aug 5, 202614 min read

Linux

Why Deleting a ZFS Snapshot May Not Free Space

Deleting one ZFS snapshot does not mean every block visible through that snapshot becomes free. OpenZFS releases only blocks whose last remaining…

Aug 4, 20268 min read

Linux

A Full Linux Accept Queue Is Not Always a SYN Flood

TcpExtListenOverflows rose by 4,812 during a five-minute traffic burst. The kernel log mentioned a possible SYN flood, yet the packet capture showed…

Aug 4, 20269 min read

Linux

Why Linux Reports EADDRNOTAVAIL During Outbound Connection Bursts

DNS still resolves. The remote API answers from another machine. Existing sessions remain healthy, yet a Linux application logs EADDRNOTAVAIL or Cannot…

Aug 4, 20269 min read

Linux

Do Not Remount ext4 Read-Write Until the Disk Is Proven

An ext4 filesystem that suddenly becomes read-only is usually protecting data after the kernel detected a filesystem or storage error. Do not…

Aug 4, 20269 min read

Linux

Linux RAID Recovery Speed Has a Production Latency Budget

Two clocks run during Linux md RAID recovery: the array must regain redundancy, while production requests still have latency objectives. The safe…

Aug 4, 202610 min read

Linux

Maildir Can Run Out of Inodes While Disk Space Looks Free

A Dovecot server can reject new mail with No space left on device while df -h still reports gigabytes free. Maildir stores…

Aug 4, 202610 min read

Linux

Packets Can Drop Inside Linux Before the Application Sees Them

An interface can remain UP, the process can keep listening, and Linux can still discard receive packets before they reach the application…

Aug 4, 202611 min read

Linux

Low Host Utilization Does Not Rule Out Container CPU Throttling

Low host CPU utilization does not prove that a container has CPU time available. A cgroup v2 limit in cpu.max is enforced…

Aug 3, 20269 min read

Security

Rotate SSH Host Keys Without Locking Out VPS Access

Do not overwrite active SSH host-key files in one step. Generate replacement keys under new filenames, load old and new identities together,…

Aug 3, 20269 min read

AI & Machine Learning

Why Ollama Uses CPU Even When Your GPU Is Available

nvidia-smi can show a healthy GPU while an Ollama request still runs partly—or entirely—on CPU. That contradiction does not have one universal…

Aug 3, 202610 min read

Linux

Linux Conntrack Is Full While Existing Sessions Still Work

One SSH session remains responsive, a database connection keeps serving queries, yet every fresh health check times out. That combination can look…

Aug 3, 202611 min read

Linux

Fix Linux VPS Clock Drift Without Breaking Running Services

Clock drift rarely introduces itself as “clock drift.” It arrives as a certificate that is “not yet valid,” an expired login token…

Aug 2, 202612 min read

DevOps

Cloud-Init Says Done, but Your VPS Is Not Ready

A new VPS can carry three different clocks. The provider may label it running when the virtual machine starts, cloud-init may report…

Aug 2, 202610 min read

Linux

Why systemd Stops Restarting a Failed Service

start-limit-hit is not the reason your application failed. It means systemd observed too many start attempts inside the unit's configured interval and…

Aug 2, 202610 min read

Linux

When CPU Steal Time Slows Your VPS

CPU steal time is the share of time a virtual CPU was ready to work but could not run because the hypervisor…

Aug 2, 202611 min read