Known & Common Errors

posix_openpt failed: Device not configured

<exited with error: posix_openpt failed: Device not configured>

Caution

macOS has a limit on the number of pseudo-terminal (PTY) devices available. This also causes fork failed: Device not configured errors in tmux.

Cause: You have too many terminal sessions open.

Solution 1: Close unused terminals

The quickest fix. Close terminal tabs, panes, or tmux sessions you are not actively using.

Solution 2: Increase the PTY limit

The default macOS PTY limit is typically 127. You can increase it:

# Check current PTY limit
sysctl kern.tty.ptmx_max

# Increase for current session (requires sudo)
sudo sysctl -w kern.tty.ptmx_max=512

To make it permanent across reboots, add to /etc/sysctl.conf:

kern.tty.ptmx_max=512

Deleted files appear greyed out

Note

This is expected behavior. The file is marked for deletion in Git. It has been deleted from the working directory but the deletion has not yet been committed.

Process or file descriptor limits

If terminals fail to open or processes fail to start without the posix_openpt error above, you may have hit your file descriptor or process limit.

Diagnose:

# Check current limits
ulimit -n   # file descriptors (default 256 on macOS - too low)
ulimit -u   # max user processes

Fix:

# Increase file descriptor limit (current session)
ulimit -n 10240

# Increase max user processes if needed (current session)
ulimit -u 65536

Tip

To make this permanent, add the ulimit commands to your ~/.zshrc or ~/.bashrc.