wezterm

WezTerm — High-RAM Agent Swarm Management

Core Principle: WezTerm mux replaces tmux. Leverage massive RAM (512GB+) for agent swarms. Never nest multiplexers.

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Quick Diagnosis

# One-liner status
echo "Mux: $(ps aux | grep -c '[w]ezterm-mux') procs | $(wezterm cli list --format json 2>/dev/null | jq length) panes | RSS: $(ps -eo rss,args | grep '[w]ezterm-mux' | awk '{sum+=$1} END {printf "%.1fGB", sum/1024/1024}')"

# Is mux running?
ps aux | grep wezterm-mux | grep -v grep

# Memory usage
ps -eo pid,rss,args | grep wezterm-mux | awk '{printf "%.1fGB\n", $2/1024/1024}'

# Recent logs
tail -20 /run/user/$(id -u)/wezterm/wezterm-mux-server-log-*.txt

# Connection test
wezterm cli list --format json | jq length

# Socket status
ls -la /run/user/$(id -u)/wezterm/sock

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The Agent Swarm Problem

When running 20+ AI agents (Claude Code, Codex, Gemini CLI), each agent produces continuous output, runs for hours, spawns subprocesses, and operates in parallel. This overwhelms WezTerm's defaults.

┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃                          THE FAILURE CASCADE                                  ┃
┃                                                                               ┃
┃  1. Output buffer fills        →  parser falls behind                         ┃
┃  2. Coalesce delay accumulates →  lag builds up                               ┃
┃  3. Caches thrash              →  CPU spikes on render                        ┃
┃  4. Socket buffers fill        →  connection hangs                            ┃
┃  5. You restart mux            →  ALL SESSIONS DIE (use reptyr first!)        ┃
┃                                                                               ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

Default Assumptions vs Reality

WezTerm Assumes	Reality with Agent Swarms
~100 lines/sec	1,000+ lines/sec across panes
Occasional scrollback access	Scrollback is primary debug tool
Few panes	20+ panes, all active
Cache hits common	Rapid context switches = cache misses

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Performance Tuning (High-RAM)

THE EXACT PROMPT — Auto-Tune for Your RAM

# Auto-tune using linear interpolation (recommended)
curl -fsSL https://raw.githubusercontent.com/Dicklesworthstone/misc_coding_agent_tips_and_scripts/main/wezterm-mux-tune.sh | bash

# Preview without applying
./wezterm-mux-tune.sh --dry-run

# Calculate for specific RAM
./wezterm-mux-tune.sh --ram 200

# Use exact fixed profile
./wezterm-mux-tune.sh --profile 512

# Restore from backup
./wezterm-mux-tune.sh --restore

THE EXACT PROMPT — 512GB Manual Profile

Add to ~/.wezterm.lua before return config:

-- 512GB HIGH-RAM PROFILE
config.scrollback_lines = 10000000
config.mux_output_parser_buffer_size = 16 * 1024 * 1024
config.mux_output_parser_coalesce_delay_ms = 1
config.ratelimit_mux_line_prefetches_per_second = 1000
config.shape_cache_size = 65536
config.line_state_cache_size = 65536
config.line_quad_cache_size = 65536
config.line_to_ele_shape_cache_size = 65536
config.glyph_cache_image_cache_size = 4096

Settings Quick Reference

Setting	Default	512GB	Purpose
scrollback_lines	3,500	10M	History per pane
mux_output_parser_buffer_size	128KB	16MB	PTY batch buffer
mux_output_parser_coalesce_delay_ms	3	1	Parse latency
ratelimit_mux_line_prefetches_per_second	50	1000	Scroll speed
shape_cache_size	1,024	65,536	Font cache
line_state_cache_size	1,024	65,536	Line attr cache
line_quad_cache_size	1,024	65,536	GPU geometry
glyph_cache_image_cache_size	256	4,096	Rasterized glyphs

Profiles by RAM

RAM	scrollback	buffer	caches	prefetch	Memory footprint
64GB	1M	2MB	8K	500	3-8 GB
128GB	2M	4MB	16K	750	5-15 GB
256GB	5M	8MB	32K	500	8-25 GB
512GB	10M	16MB	64K	1000	15-60 GB

After applying: Restart mux to load new settings.

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Emergency Session Rescue

Scenario: Mux unresponsive but agents still running. DON'T kill mux yet!

THE EXACT PROMPT — reptyr Rescue Workflow

# 1. Connect via plain SSH (bypass broken mux)
ssh user@host

# 2. Setup
sudo apt-get install -y reptyr
sudo sysctl -w kernel.yama.ptrace_scope=0

# 3. Create rescue session
tmux new-session -d -s rescue -x 200 -y 50

# 4. Find agents
ps -eo pid,args | grep -E 'claude --dangerously|codex --dangerously' | grep -v grep

# 5. Migrate each agent
for pid in $(ps -eo pid,args | grep -E 'claude --dangerously|codex --dangerously' | grep -v grep | awk '{print $1}'); do
  tmux new-window -t rescue -n "agent-$pid"
  tmux send-keys -t "rescue:agent-$pid" "reptyr -T $pid" Enter
  sleep 0.5
done

# 6. Verify migrations
for win in $(tmux list-windows -t rescue -F "#{window_name}" | grep agent); do
  tmux capture-pane -t "rescue:$win" -p | grep -qE "bypass|Claude" && echo "✓ $win" || echo "✗ $win"
done

# 7. NOW safe to kill mux
pkill -9 -f wezterm-mux

# 8. Restore security
sudo sysctl -w kernel.yama.ptrace_scope=1

# 9. Restart mux
wezterm-mux-server --daemonize

# 10. Access rescued agents
tmux attach -t rescue  # Ctrl-b w to browse

reptyr Failure Modes

Error	Cause	Fix
"Operation not permitted"	ptrace blocked	sudo sysctl -w kernel.yama.ptrace_scope=0
"shares process group"	Process has children	Use reptyr -T (not plain reptyr)
"Unable to attach"	Additional protections	Cannot migrate; will be lost

Success rate: 50-70%. Older/idle sessions migrate better than active ones with many subprocesses.

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Mux Server Operations

Start/Stop

# Start (daemonized)
wezterm-mux-server --daemonize

# Stop gracefully
pkill -f wezterm-mux-server

# Force stop (kills sessions!)
pkill -9 -f wezterm-mux-server

# Restart (loses sessions unless rescued first)
pkill -9 -f wezterm-mux; wezterm-mux-server --daemonize

# Restart via systemd (if configured)
systemctl --user restart wezterm-mux-server

Kill Stuck Proxy Processes

Safe to kill — won't affect mux sessions:

pkill -f 'wezterm cli.*proxy'

Why Mux Degrades Over Time

Cause	Symptom	Fix
Buffer overflow	Connection timeout	Increase mux_output_parser_buffer_size
Cache thrashing	High CPU on scroll	Increase cache sizes
Session accumulation	Memory bloat	Periodic mux restart
Scrollback buildup	GB of RAM usage	Lower scrollback_lines or restart

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Persistent Sessions Setup

Remote Server (one-time)

mkdir -p ~/.config/systemd/user

cat > ~/.config/systemd/user/wezterm-mux-server.service << 'EOF'
[Unit]
Description=WezTerm Mux Server
After=network.target

[Service]
Type=simple
ExecStart=/usr/bin/wezterm-mux-server --daemonize=false
Restart=on-failure
RestartSec=5
Environment=WEZTERM_LOG=warn

[Install]
WantedBy=default.target
EOF

systemctl --user daemon-reload
systemctl --user enable --now wezterm-mux-server
sudo loginctl enable-linger $USER

Local Config (SSH domain)

config.ssh_domains = {
  {
    name = 'myserver',
    remote_address = '10.0.0.1',
    username = 'ubuntu',
    multiplexing = 'WezTerm',  -- Key setting
    assume_shell = 'Posix',
  },
}

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CLI Quick Reference

Task	Command
List panes	wezterm cli list
List panes (JSON)	wezterm cli list --format json
Split right	wezterm cli split-pane --right
Split bottom	wezterm cli split-pane --bottom
Send text	wezterm cli send-text --pane-id N "cmd\n"
New tab	wezterm cli spawn
New tab in domain	wezterm cli spawn --domain-name SSH:host
Connect to mux	wezterm connect unix
Zoom toggle	wezterm cli zoom-pane --toggle

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Maintenance Checklist

• Weekly: Check mux memory, consider restart if > 50GB RSS
• Before restart: Check for active agents (use reptyr if needed)
• After tuning: Restart mux to apply new settings
• Version mismatch: Client/server MUST match exactly

# Check version match
wezterm --version                    # local
ssh host 'wezterm --version'         # remote

# Check mux memory
ps -eo rss,args | grep '[w]ezterm-mux' | awk '{printf "RSS: %.1fGB\n", $1/1024/1024}'

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Troubleshooting

Symptom	Cause	Fix
Connection timeout	Buffer overflow	Increase mux_output_parser_buffer_size
Laggy scrolling	Low prefetch rate	Increase ratelimit_mux_line_prefetches_per_second
High CPU on render	Cache thrashing	Increase all cache sizes
Truncated history	Small scrollback	Increase scrollback_lines
"Broken pipe" in logs	Client disconnect	Check network stability
"Checking server version" hangs	Mux overloaded	Rescue sessions, restart mux
Version mismatch error	Client/server differ	Update both to same version

Log Locations

# Mux server log
/run/user/$(id -u)/wezterm/wezterm-mux-server-log-*.txt

# Socket path
/run/user/$(id -u)/wezterm/sock

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References

Topic	File
Full CLI commands	COMMANDS.md
Persistent sessions deep-dive	PERSISTENT-SESSIONS.md
Performance tuning deep-dive	PERFORMANCE-TUNING.md