screen Command on Mac: Stuck at 4.00.03, 2 Script Traps
The screen command on Mac is already installed, and it is old. On the Mac mini that runs this business, /usr/bin/screen -v prints Screen version 4.00.03 (FAU) 23-Oct-06 on macOS 26.4.1, and then exits with status 1. GNU has released 17 versions since that one, the latest being 5.0.2 on 2026-07-11. Apple has shipped ten builds of its copy without moving the version.
I mapped every macOS release in Apple's distribution-macOS repository to a tag of Apple's screen project, ran the stock binary next to Homebrew's 5.0.2 on this machine, and read 82 Stack Exchange questions tagged gnu-screen and macOS. Two of the problems I found are not in any of those questions.
Which screen does macOS ship?
Apple's screen repository has 13 tags. I read patchlevel.h in each one and matched them to 166 distribution-macOS tags through the screen submodule pointer. 151 of those tags contain screen. Mac OS X 10.2 shipped 3.9.10, 10.3 shipped 3.9.15 and 10.4 shipped 4.0.2. From 10.4.10 in 2007 to macOS 26.5, every release ships 4.0.3.
The ten 4.0.3 builds are not identical. Diffing the tags shows what Apple changed. The socket directory moved to your per-user temp folder in an __APPLE__ block that calls confstr(_CS_DARWIN_USER_TEMP_DIR). screen-24 (macOS 11) added a clear-library-validation entitlement, which codesign -d --entitlements - still shows on the installed binary. screen-29, dated 2022-01-11 and shipped from macOS 13.0 on, wraps format strings in fmtcheck(). Nothing has changed since. The binary is a universal x86_64/arm64e file signed by Apple, mode -rwxr-xr-x, so it is not setuid.
What 4.00.03 can and can't do
I started both versions inside a tmux pane on this Mac with TERM=xterm-256color and LANG=en_US.UTF-8, then sent keys to them.
| Feature | Added upstream | /usr/bin/screen 4.00.03 | Homebrew 5.0.2 |
|---|---|---|---|
Vertical split, C-a | | 4.2.0 (2014) | Nothing happens | Splits the window |
-Q to query a session | 4.2.0 (2014) | Error: Unknown option -Q | -Q echo hi prints hi |
truecolor on | 5.0.0 (2024) | Not available | Available |
| 256 colors | Before 4.0.3 | tput colors = 256 | 256 |
| UTF-8 output (é, 한) | Before 4.0.3 | Correct with LANG set | Correct |
-dmS, -r, -X, -ls | Before 4.0.3 | Work | Work |
Inside both, $TERM came out as screen.xterm-256color. That matters because the most-viewed Mac screen question on Stack Overflow, at 33,853 views, is Cannot find termcap entry for 'xterm-256color' from 2012. On macOS 26.4.1 that error didn't appear. The missing vertical split is the second most-viewed Mac question, Vertical Split in GNU Screen on Mac OS X (25,321 views), and on stock macOS it is still missing.
Trap 1: two screens, two socket folders
If you install Homebrew's screen, you now have two, and they can't see each other's sessions. Apple's build keeps sockets in $TMPDIR/.screen. Homebrew's keeps them in ~/.screen. I started one session with each:
$ /usr/bin/screen -dmS s1 sleep 600
$ /opt/homebrew/bin/screen -dmS b1 sleep 600
$ /usr/bin/screen -ls
There is a screen on:
77755.s1 (Detached)
1 Socket in /var/folders/nw/1f_hl8c90g54vr86ph4dzjth0000gn/T/.screen.
$ /opt/homebrew/bin/screen -ls
There is a screen on:
77751.b1 (Detached)
1 Socket in /Users/sg-mini/.screen.
$ /opt/homebrew/bin/screen -r s1
There is no screen to be resumed matching s1.Which one you get depends on PATH. An interactive shell with Homebrew set up finds /opt/homebrew/bin/screen first. A script, a cron job or a launchd job that only has /usr/bin:/bin finds Apple's. So a session you start by hand looks gone when a script checks for it, and the other way round. The fix is to call one binary by its full path everywhere.
I expected a second problem here and didn't find it. Because the socket folder comes from TMPDIR, I thought a job with no TMPDIR in its environment, like a launchd job, would look in a different place. It doesn't. env -u TMPDIR screen -ls and env -i HOME=$HOME PATH=/usr/bin:/bin screen -ls both listed the same two sessions in the same /var/folders/…/T/.screen, because Apple's code asks the system for the folder instead of reading the variable. That was as my own user. The binary also contains the old /tmp/screens and /tmp/uscreens paths, and I didn't test which one it uses under sudo.
Trap 2: exit codes you can't use
The second problem is for anyone scripting screen, which is what you do when you start long jobs on a headless Mac over SSH. I ran each command with zero, one, two and three detached sessions:
| Command | 4.00.03 exit code | 5.0.2 exit code |
|---|---|---|
screen -v | 1 | 0 |
screen -ls, sessions running | 1 | 0 |
screen -ls, none running | 1 | 1 |
screen -q -ls, 0 / 1 / 3 detached | 8 / 10 / 10 | 9 / 11 / 13 |
screen -S s1 -X bogusxyz | 0 | 0 |
screen -S nosuch -X quit | 1 | 1 |
On Apple's build, screen -ls && echo running never prints, even when sessions exist. The -q -ls form is documented in the GNU ChangeLog as returning 10 plus the number of detached sessions. 5.0.2 does that. 4.00.03 returned 10 for one session and 10 again for three. Argument order matters too. screen -ls -q treats -q as a session name to match, and printed No Sockets found while two sessions were running. And -X returned 0 for a command that doesn't exist, so it can't tell you whether your command worked either.
What did work as a yes/no test on Apple's build was sending a harmless command to the session by name:
if /usr/bin/screen -S job1 -X select . ; then
echo "job1 is running"
fiThat returned 0 with job1 running and 1 with No screen session found. when it wasn't. The same -X to a missing session also returned 1 on 5.0.2.
Install Homebrew's screen, or use tmux?
Homebrew's screen formula was a 513 KB bottle download with nothing else to install here, and brew uninstall screen removed it cleanly. It is the version to use if you want vertical splits or -Q. If you install it, kill any sessions from the old one first and stop calling bare screen from scripts.
On security, SUSE's May 2025 review found five CVEs that 5.0.1 fixed. The root exploit and several others depend on screen being installed setuid-root, and their matrix covers Linux distributions and BSDs. macOS appears only in a footnote about NetBSD's pkgsrc packages, not Apple's build. Neither the Apple binary nor the Homebrew bottle is setuid on this Mac, so those didn't apply, and I didn't test the rest against 4.00.03.
This machine runs its long jobs in tmux, not screen. That was decided before any of this testing, so it isn't a verdict on screen. Still, everything above is a problem tmux doesn't have here, because there is only one tmux on this Mac. How Claude Code behaves inside tmux is covered in Claude Code tmux. If you only need a job to survive a closed SSH session and don't need to reattach, nohup on Mac may be enough.
What Mac users ask about screen
The Stack Exchange API returned 82 questions tagged both gnu-screen and macOS across Stack Overflow (36), Super User (38), Unix & Linux (8) and Server Fault (5 under the old osx tag, 0 under macos), with 337,953 views in total. Sorted by title keyword, 20 are about terminal display (termcap, colors, UTF-8, resizing) with 110,078 views, and 13 are about the shell environment inside screen (PATH, profile, working directory). Six are about serial ports, with 44,970 views, because screen /dev/cu.usbserial-XXXX 115200 is the usual way to talk to a serial device from a Mac. The adapters that work without a driver are in USB to serial adapter for Mac. Four are about splits and 27 didn't fit a group.
67 of the 82 were asked between 2009 and 2015, and the newest is from 2022. None of them mention the two-socket-folder problem or the exit codes. That fits a tool people stopped installing a second copy of. The same Apple-tag method also explains why xxd on Mac has seven versions while screen has had one since 2007.
FAQ
Is the screen command installed on Mac?
Yes. macOS includes GNU screen at /usr/bin/screen, so there is nothing to install. Every release from Mac OS X 10.4.10 to macOS 26.5 ships version 4.00.03, dated 2006. It lacks vertical splits, the -Q flag and truecolor, which arrived in later GNU releases. Homebrew's screen formula installs the current 5.0.2.
How do I use the screen command on Mac?
Run screen -S name to start a named session, press Ctrl-a then d to detach, and run screen -r name to reattach. screen -ls lists sessions. To start a job without attaching, use screen -dmS name command. On Apple's build, screen -ls exits 1 even when sessions exist, so scripts should test with screen -S name -X select . instead.
Why can't I split screen vertically on Mac?
The screen in macOS is version 4.00.03, and vertical split (Ctrl-a | or split -v) was added in GNU screen 4.2.0 in 2014. Install a newer screen with brew install screen and run /opt/homebrew/bin/screen, or use tmux. Sessions started by one version are not visible to the other, because they keep sockets in different folders.
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How this was checked: all commands were run on 2026-10-15 on a Mac mini M4 running macOS 26.4.1, comparing /usr/bin/screen with Homebrew's screen 5.0.2 bottle, which I installed for the test and then uninstalled. Key-press tests ran inside a separate tmux server with the output captured from the pane. The version map comes from patchlevel.h in all 13 tags of apple-oss-distributions/screen, matched by commit to the screen submodule in 166 distribution-macOS tags (151 include screen). That is the source Apple published, and I only checked the installed binary on this one Mac. Upstream dates are from ftp.gnu.org and the 4.2.0 and 5.0.x ChangeLogs. Stack Exchange numbers come from the API on the same day, with titles grouped by keyword.