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Welcome to InfoTech Ninja

IT professional writing about cybersecurity, cloud & DevOps, automation, networking, and systems administration. Real-world guides for real-world problems.

#Cybersecurity #Cloud #Automation #Networking #SysAdmin

Latest Articles

Linux Admin

Linux Performance & Observability: load, latency tails, perf top, eBPF

Working reference for the 10 most common Linux performance problems. High load with low CPU (D-state iowait), p99 latency tails (averages lie), high context switch rate, disk I/O saturation (%util / await), network at line rate, memory pressure without OOM (vmstat si/so), slow boot (systemd-analyze blame), hung app (strace / wchan / stack), kernel CPU vulnerability mitigations, cloud noisy neighbor (%steal). Tools: vmstat / iostat / sar / perf top / bcc-eBPF / biolatency / execsnoop. Cross-linked to monitoring command reference.

• 3 min read
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Linux Admin

Linux CI/CD & Automation Errors: runners, secrets, flaky tests, deploy failures

Working reference for the 10 most common Linux CI/CD pipeline errors. Runner offline (gitlab-runner / github-actions-runner systemctl), secret env var not injected, docker login failures (use ephemeral CI tokens), flaky tests (env vs hardware vs race), build cache miss, disk full on runner, job timeouts, deployment connection refused, git pull auth, Ansible host key verification. Cross-linked to docker, build, and systemd troubleshooting.

• 3 min read
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Linux Admin

Linux Database Errors: connection refused, deadlocks, replication lag

Working reference for the 10 most common Linux database errors at the OS layer. PostgreSQL/MySQL/Redis: connection refused (systemctl status), too many connections (PgBouncer / pool), password auth (pg_hba.conf), deadlocks (pg_stat_activity + pg_blocking_pids), replication lag, archive_command failures, MySQL Lost connection (max_allowed_packet, wait_timeout), Redis maxmemory eviction policy, disk full on data dir, long-running stuck transactions. Cross-linked to process/memory and networking troubleshooting.

• 3 min read
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Linux Admin

Linux Programming & Build Errors: gcc, ld, missing headers, ABI mismatch

Working reference for the 10 most common Linux build/compile/link errors. fatal error: header not found (install -dev / -devel), undefined reference (link order matters), library not found at runtime (ldd / LD_LIBRARY_PATH / ld.so.conf.d), GLIBC ABI mismatch (build in target container), segfault in tests, missing make/cmake (build-essential), Python ModuleNotFoundError, npm ENOSPC, exec on noexec mount, OOM during compile (lower -j, swap).

• 3 min read
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Linux Admin

Linux Advanced Networking Errors: PMTU, conntrack, VLAN, bonding

Working reference for 10 advanced Linux networking issues that show up at scale. PMTU black-hole in tunnels (clamp MSS), conntrack table full on busy NAT/LB boxes (sysctl + timeout tuning), VLAN tag mismatches, bond failover not working (LACP vs active-backup), bridge / STP, NAT masquerade not forwarding, rogue IPv6 RA, ssh slow connect (UseDNS no), asymmetric routing, jumbo frame end-to-end requirements. Cross-linked to networking command reference.

• 3 min read
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Linux Admin

Linux Security Errors: SELinux denies, expired certs, firewall blocks, fail2ban

Working reference for the 10 most common Linux security errors. SELinux AVC denial (ausearch + audit2allow + restorecon), AppArmor DENIED (aa-complain + aa-genprof), TLS cert expired (certbot timer), firewall blocking expected traffic with iptables -L -nv counter diagnosis, fail2ban banned-IP recovery, SSH brute force defenses (key-only / fail2ban / port move), sudo timeout in long scripts, NET::ERR_CERT_REVOKED, audit log full, GPG signature verification. Cross-linked to auth errors, file permissions, and networking errors.

• 3 min read
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Linux Admin

Linux Storage & RAID Errors: mdadm degraded, LVM, SMART, multipath

Working reference for the 10 most common Linux storage and RAID failures. mdadm degraded array (remove + add), the worst-case dual-disk failure during rebuild, LVM volume group not found (vgscan + vgchange), thin pool 100% full, SMART pre-fail attributes (replace before catastrophic), multipath all-paths-failed, snapshot CoW pool overflow, force-assemble of broken arrays as last resort, iSCSI session loss, fstrim discard support. Cross-linked to disk/filesystem command reference and performance troubleshooting.

• 3 min read
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Linux Admin

Linux Kernel & Boot Errors: GRUB, kernel panic, initramfs, emergency mode

Working reference for the 10 most common Linux boot failures. Kernel panic - not syncing (UUID/initramfs/hardware), GRUB file not found, VFS unable to mount root (post-disk-replace UUID change), systemd emergency mode from failed mount, no init found, missing initramfs modules, fsck during boot, OOM in initramfs on small VMs, kernel command line parse errors, silent boot loops. Cross-linked to disk/filesystem and storage/RAID.

• 3 min read
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