Desktop app leaks PTY masters until system PTY limit (511) is exhausted — Terminal fails with 'forkpty: Device not configured'

Summary

The Claude desktop app (/Applications/Claude.app) leaks pseudo-terminal (PTY) master file descriptors over its runtime. After ~1.5 days of uptime a single app process held 506 of the system's 511 available PTYs (kern.tty.ptmx_max = 511). Once the limit is reached, no other application can open a PTY — opening Terminal.app fails immediately with:

[forkpty: Device not configured]
[Could not create a new process and open a pseudo-tty.]

This makes the whole machine's terminal usage unusable until the Claude app is quit, even though the OS itself is healthy (plenty of disk, /dev/ptmx present, devfs mounted, process/file limits fine).

Environment

• Claude desktop app: 1.14271.0
• Claude Code (bundled): 2.1.181
• macOS: 26.2 (25C56), Apple Silicon
• kern.tty.ptmx_max: 511 (macOS default)

Evidence

App process (PID 679) had been running ~34h:

$ ps -o lstart=,etime= -p 679
Sun Jun 21 11:37:25 2026     01-09:57:48

It alone held 506 PTY masters:

$ lsof /dev/ptmx | awk 'NR>1{print $1,$2}' | sort | uniq -c | sort -rn | head
 506 Claude 679
   5 Code\x20H 1147
   1 COMMAND

$ lsof -p 679 | grep -c /dev/ptmx
506

Slave device nodes were exhausted up to the limit:

$ ls /dev/ttys* | wc -l
527

All other system health checks were clean:

• Disk: 60 GB free
• /dev/ptmx: crw-rw-rw- root tty present
• devfs mounted on /dev
• kern.maxproc 4000, kern.maxfiles 122880 — far from limits

Impact

• Every new PTY consumer on the machine fails: Terminal, iTerm, tmux, script, IDE integrated terminals, SSH -t, etc.
• Presents as a scary, opaque system error (forkpty: Device not configured) that gives no hint the Claude app is responsible.
• Only workaround is to fully quit (Cmd+Q) and relaunch the Claude app, which releases all leaked PTYs at once.

Expected behavior

PTY master FDs spawned for terminal/MCP/sub-sessions should be closed when those sessions end, so the count stays bounded over long app uptimes rather than growing monotonically toward the 511 ceiling.

Reproduction (likely)

1. Keep the Claude desktop app running for an extended period (~1+ days) with normal Claude Code / terminal / MCP usage.
2. Observe lsof -p <Claude PID> | grep -c /dev/ptmx growing over time and not dropping when sessions close.
3. Once it nears 511, opening Terminal.app fails with forkpty: Device not configured.

Notes

Possible mitigation on the user side (non-persistent, does not fix the leak): sudo sysctl -w kern.tty.ptmx_max=2048. Real fix is releasing the PTY masters when their sessions end.