#Cron
The Monitor That Hammered Devices Until the Whole Farm Went Down
A monitoring loop that runs every 30 seconds and tries to recover every device that fails a ping sounds useful, until one device hangs and gets hammered repeatedly until the whole bus goes down. This article walks through ruling out hardware, tracking what was accessing the devices, and the settings that fixed it.
No kWh Meter? Estimate Daily Electricity Costs from Current
Notes on converting CT current readings into energy usage and daily time-of-use electricity costs, from the three-phase power formula and the sampling interval built into it, through skipping outages and separating peak from off-peak with epoch arithmetic, to a daily summary table that made the web page seven times faster.
Ingesting Mail Without Disrupting Someone Else's Mailbox
The mailbox the app fetches from is one people actually use every day — fetching with UNSEEN silently misses mail when the owner reads it on their phone before cron runs. The right approach is UID SEARCH paired with UIDVALIDITY and BODY.PEEK, with deduplication handled on our side.
Reads from a Replica Must Show How Many Minutes Old the Data Is
replication can report a lag of 0 seconds while the data is stuck at yesterday, because these two signals measure different things — how to set up a monitor that checks both Seconds_Behind_Master and business data freshness, catches anyone writing directly to the slave, and has another check watching the monitor itself
The App Uses UTC, People Use Thai Time — 7 Hours Off, No Errors
Scheduled for three in the afternoon, published at ten at night. No errors, nothing wrong in the logs, because the app stores UTC while the person entering the time thinks in Thai time. This article traces the issue from an env setting that has no effect to the single line that writes Thai wall-clock time into a column everyone reads as UTC.
The Service Is Running but Dead — systemd restart Cannot Help
A long network outage broke DNS. A daemon holding a session with an external API failed to log in 194 times, then hung halfway through the process. It never exited, so the system never restarted it — why I stopped checking whether a process was alive and started measuring data freshness instead.
A 25-Hour Power Outage Left Scheduled Jobs Missing
The machine running my automated jobs lost power three times in three days, with the longest outage lasting 25 hours. When it came back, I found that jobs scheduled directly through Task Scheduler had skipped their runs entirely, while jobs managed by a dispatcher that checked the time itself had all caught up. This article covers the setting to enable, what to avoid during recovery, and the traps that led me to misread the status.
Every Layer Reported Success While the Output Was Garbage
In one day, four layers of the same automated pipeline failed together, but every layer reported success without a single error line. The person who caught it was a user who said the site was not updating. These are the rules I wrote afterward so that failing stages could speak up for themselves.
Every File Is Backed Up, but I Still Can't Rebuild the Server
The database dump is complete, the code tar is complete, and all the secrets are there, but put them on a blank machine and the site will not come up, because the things that actually make the server work were never in the backup files. This article lists what disappears with the machine and the recovery sequence I wrote for my future self.
Backups Succeeded Nightly, but Offsite Uploads Failed for 3 Weeks
cron ran every night, local files were complete every day, and the log said done, but offsite storage had not changed for 3 weeks. The first 8 nights of backups were already gone for good because local rotation had deleted them first. This article examines the two gaps that let the failure stay silent for so long.
The Web User's crontab Isn't the One Running Your Jobs
Schedule changes saved through the web still leave jobs running at the old times because the script writes the web user's crontab, not the user’s crontab that cron actually reads. How to spot it in 3 commands, the sudoers drop-in I used, and how to design it so this cannot happen again.
Laravel Queues on Shared Hosting — Don't Share Redis with Cache
If you're enabling queues for Laravel on shared hosting and planning to separate the queue from cache with different REDIS_DB numbers, that won't help. maxmemory and eviction apply to the whole instance, not individual DBs. This article explains why I chose the database driver instead, with complete systemd units to replace Supervisor.
My Firewall Permanently Banned Googlebot and Hid Sites from Search
I investigated why sites disappeared from search results and found Googlebot in my own firewall's permanent ban list. 408 of 500 entries came from the counter tallying WAF false positives. How I lifted the bans, wrote a script to fetch official bot IP ranges into the ignore list daily, and dealt with a grep trap and the side effects of blocking entire countries.
Factory to Cloud Behind NAT: Push Snapshots and a Command Queue
The production machine sits in a LAN behind NAT with no public IP, but the owner wants to view data on a cloud website and make edits from a phone that reach the internal machine — possible without opening ports or setting up a VPN, using push snapshots + an edit command queue + idempotent acks
One Query Hung for 54 Minutes, Causing Sitewide 504s via MyISAM Locks
A single 30 MB table caused 504s on every page across the site, even with 9.5 GB of RAM still free — I traced information_schema.PROCESSLIST to a single SELECT that had been stuck for 54 minutes on a MyISAM table, cascading into metadata locks across the server, with an immediate fix and ways to prevent it from happening again.
Set DirectAdmin Admin Backup Cron from the CLI Without the Panel
CMD_ADMIN_BACKUP takes five steps to set up a cron job, but DirectAdmin actually just appends one line to backup_crons.list and lets dataskq pick it up. Here is how to write directly to the file from the CLI, including common traps with when=now, base64, and append_to_path.
Off-Site Backups with Pull Architecture + rclone/rsync
Add off-site Layer 3 to complete 3-2-1 with pull architecture (the destination host fetches the data), rclone + rsync, and lessons from real pitfalls involving NAT, RSA host keys, cwRsync, and PID recycling.
Rebuilding DirectAdmin Backups with NFS and POSIX ACL in Production
A record of rebuilding backups on a DirectAdmin server after migrating to a new machine — from FTP push that broke at three layers to an NFSv4 hard mount + POSIX ACL, with kernel-level lessons learned along the way.
Per-User Redis on DirectAdmin Without Buying pro_pack
How to set up per-user Redis object cache on DirectAdmin shared hosting with a systemd template + unix socket + cgroup limit, using a custom provisioning script instead of the DA panel that requires a pro_pack license, with connection recipes for WordPress, Flarum, and Laravel
Tuning ModSecurity on DirectAdmin for Shared Hosting
The 4 additions I made beyond DA defaults — exclusions before CRS, a 1-hit credscan ban, a fix for the incorrect MODSEC_LOG path shipped by DA, and a self-heal cron to recover from rebuild overwrites