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108 lines
4.4 KiB
Markdown
108 lines
4.4 KiB
Markdown
---
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title: Mastodon Instance Tuning
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domain: selfhosting
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category: services
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tags:
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- mastodon
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- fediverse
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- self-hosting
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- majortoot
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- docker
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status: published
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created: 2026-04-02
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updated: 2026-04-30T05:21
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---
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# Mastodon Instance Tuning
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Running your own Mastodon instance means you control the rules — including limits the upstream project imposes by default. These are the tweaks applied to **majortoot** (MajorsHouse's Mastodon instance).
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## Increase Character Limit
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Mastodon's default 500-character post limit is low for longer-form thoughts. You can raise it, but it requires modifying the source — there's no config toggle.
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The process depends on your deployment method (Docker vs bare metal) and Mastodon version. The community-maintained guide covers the approaches:
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- [How to increase the max number of characters of a post](https://qa.mastoadmin.social/questions/10010000000000011/how-do-i-increase-the-max-number-of-characters-of-a-post)
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**Key points:**
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- The limit is enforced in both the backend (Ruby) and frontend (React). Both must be changed or the UI will reject posts the API would accept.
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- After changing, you need to rebuild assets and restart services.
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- Other instances will still display the full post — the character limit is per-instance, not a federation constraint.
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- Some Mastodon forks (Glitch, Hometown) expose this as a config option without source patches.
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## Media Cache Management
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Federated content (avatars, headers, media from remote posts, preview cards) gets cached in S3. On an active single-user instance federating with large servers, this grows fast — the `majortoot` bucket hit **648 GB** with only ~7 GB of actual local content. The other ~620 GB was remote cache.
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### Check current usage
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```bash
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# Bare metal (rbenv)
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export PATH="$HOME/.rbenv/bin:$HOME/.rbenv/shims:$PATH"
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cd /home/mastodon/live
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RAILS_ENV=production bin/tootctl media usage
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```
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Output breaks down by type with local vs total — the gap between those two numbers is all purgeable remote cache.
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### Manual prune
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Run these three commands to clear all remote cache types:
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```bash
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export PATH="$HOME/.rbenv/bin:$HOME/.rbenv/shims:$PATH"
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export RAILS_ENV=production
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cd /home/mastodon/live
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# 1. Remote media attachments older than 7 days
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bin/tootctl media remove --days=7 --concurrency=5
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# 2. Remote avatars and headers (accounts not followed/following locally)
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bin/tootctl media remove --prune-profiles --remove-headers --days=7 --concurrency=5
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# 3. Preview card thumbnails older than 30 days
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bin/tootctl preview_cards remove --days=30 --concurrency=5
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```
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> **Note:** On a large cache (hundreds of GB, millions of objects), each command can take 30–60+ minutes. Run in `tmux` to survive SSH disconnection.
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### Automate with weekly cron
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Deploy via `configure_mastodon_media_prune.yml` Ansible playbook. It installs a wrapper script and cron entry for the `mastodon` user.
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Manual crontab entry:
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```
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0 3 * * 0 /home/mastodon/media-prune.sh
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```
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Log output goes to `/var/log/mastodon/media-prune.log`.
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### Reduce S3 storage class costs
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By default Mastodon uploads to S3 Standard ($0.023/GB/mo). Switching to Standard-IA halves the storage cost for infrequently accessed media:
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```bash
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# In /home/mastodon/live/.env.production
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S3_STORAGE_CLASS=STANDARD_IA
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```
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Then restart Mastodon. New uploads will use Standard-IA ($0.0125/GB). Note the 30-day minimum charge per object — fine for media attachments, less ideal for very short-lived objects.
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### What is and isn't removed
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- ✅ **Removed:** Cached copies of remote users' media, avatars, headers, preview card thumbnails
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- ✅ **Re-fetched on demand:** Remote media is pulled again if someone views the post
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- ❌ **Never removed:** Your local posts' media, your account's avatar/header, Mastodon account export backups (`/backups/`)
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- ❌ **Not affected:** PostgreSQL database, local disk usage outside S3
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## Gotchas & Notes
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- **Character limit changes break on upgrades.** Any source patch gets overwritten when you pull a new Mastodon release. Track your changes and reapply after updates.
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- **`tootctl` is your admin CLI.** It handles media cleanup, user management, federation diagnostics, and more. Run `tootctl --help` for the full list.
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- **Monitor disk usage.** Even with cache cleanup, the PostgreSQL database and local media uploads grow over time. Keep an eye on it.
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## See Also
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- [self-hosting-starter-guide](../docker/self-hosting-starter-guide.md)
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- [docker-healthchecks](../docker/docker-healthchecks.md)
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