macOS user IDs

2024/11/18

Context: earlier this year, Nix ran into an incompatibility with macOS Sequoia where some user IDs it was using became system reserved ones. Those user IDs that Nix used were in the 301+ range. Did macOS really, over so many years, really use up so many user IDs?

Let’s find out by looking at the system users. Here’s the /etc/passwd from macOS Sequoia.

##
# User Database
# 
# Note that this file is consulted directly only when the system is running
# in single-user mode.  At other times this information is provided by
# Open Directory.
#
# See the opendirectoryd(8) man page for additional information about
# Open Directory.
##
nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false
root:*:0:0:System Administrator:/var/root:/bin/sh
daemon:*:1:1:System Services:/var/root:/usr/bin/false
_uucp:*:4:4:Unix to Unix Copy Protocol:/var/spool/uucp:/usr/sbin/uucico
_taskgated:*:13:13:Task Gate Daemon:/var/empty:/usr/bin/false
_networkd:*:24:24:Network Services:/var/networkd:/usr/bin/false
_installassistant:*:25:25:Install Assistant:/var/empty:/usr/bin/false
_lp:*:26:26:Printing Services:/var/spool/cups:/usr/bin/false
_postfix:*:27:27:Postfix Mail Server:/var/spool/postfix:/usr/bin/false
_scsd:*:31:31:Service Configuration Service:/var/empty:/usr/bin/false
_ces:*:32:32:Certificate Enrollment Service:/var/empty:/usr/bin/false
_appstore:*:33:33:Mac App Store Service:/var/db/appstore:/usr/bin/false
_mcxalr:*:54:54:MCX AppLaunch:/var/empty:/usr/bin/false
_appleevents:*:55:55:AppleEvents Daemon:/var/empty:/usr/bin/false
_geod:*:56:56:Geo Services Daemon:/var/db/geod:/usr/bin/false
_devdocs:*:59:59:Developer Documentation:/var/empty:/usr/bin/false
_sandbox:*:60:60:Seatbelt:/var/empty:/usr/bin/false
_mdnsresponder:*:65:65:mDNSResponder:/var/empty:/usr/bin/false
_ard:*:67:67:Apple Remote Desktop:/var/empty:/usr/bin/false
_www:*:70:70:World Wide Web Server:/Library/WebServer:/usr/bin/false
_eppc:*:71:71:Apple Events User:/var/empty:/usr/bin/false
_cvs:*:72:72:CVS Server:/var/empty:/usr/bin/false
_svn:*:73:73:SVN Server:/var/empty:/usr/bin/false
_mysql:*:74:74:MySQL Server:/var/empty:/usr/bin/false
_sshd:*:75:75:sshd Privilege separation:/var/empty:/usr/bin/false
_qtss:*:76:76:QuickTime Streaming Server:/var/empty:/usr/bin/false
_cyrus:*:77:6:Cyrus Administrator:/var/imap:/usr/bin/false
_mailman:*:78:78:Mailman List Server:/var/empty:/usr/bin/false
_appserver:*:79:79:Application Server:/var/empty:/usr/bin/false
_clamav:*:82:82:ClamAV Daemon:/var/virusmails:/usr/bin/false
_amavisd:*:83:83:AMaViS Daemon:/var/virusmails:/usr/bin/false
_jabber:*:84:84:Jabber XMPP Server:/var/empty:/usr/bin/false
_appowner:*:87:87:Application Owner:/var/empty:/usr/bin/false
_windowserver:*:88:88:WindowServer:/var/empty:/usr/bin/false
_spotlight:*:89:89:Spotlight:/var/empty:/usr/bin/false
_tokend:*:91:91:Token Daemon:/var/empty:/usr/bin/false
_securityagent:*:92:92:SecurityAgent:/var/db/securityagent:/usr/bin/false
_calendar:*:93:93:Calendar:/var/empty:/usr/bin/false
_teamsserver:*:94:94:TeamsServer:/var/teamsserver:/usr/bin/false
_update_sharing:*:95:-2:Update Sharing:/var/empty:/usr/bin/false
_installer:*:96:-2:Installer:/var/empty:/usr/bin/false
_atsserver:*:97:97:ATS Server:/var/empty:/usr/bin/false
_ftp:*:98:-2:FTP Daemon:/var/empty:/usr/bin/false
_unknown:*:99:99:Unknown User:/var/empty:/usr/bin/false
_softwareupdate:*:200:200:Software Update Service:/var/db/softwareupdate:/usr/bin/false
_coreaudiod:*:202:202:Core Audio Daemon:/var/empty:/usr/bin/false
_screensaver:*:203:203:Screensaver:/var/empty:/usr/bin/false
_locationd:*:205:205:Location Daemon:/var/db/locationd:/usr/bin/false
_trustevaluationagent:*:208:208:Trust Evaluation Agent:/var/empty:/usr/bin/false
_timezone:*:210:210:AutoTimeZoneDaemon:/var/empty:/usr/bin/false
_lda:*:211:211:Local Delivery Agent:/var/empty:/usr/bin/false
_cvmsroot:*:212:212:CVMS Root:/var/empty:/usr/bin/false
_usbmuxd:*:213:213:iPhone OS Device Helper:/var/db/lockdown:/usr/bin/false
_dovecot:*:214:6:Dovecot Administrator:/var/empty:/usr/bin/false
_dpaudio:*:215:215:DP Audio:/var/empty:/usr/bin/false
_postgres:*:216:216:PostgreSQL Server:/var/empty:/usr/bin/false
_krbtgt:*:217:-2:Kerberos Ticket Granting Ticket:/var/empty:/usr/bin/false
_kadmin_admin:*:218:-2:Kerberos Admin Service:/var/empty:/usr/bin/false
_kadmin_changepw:*:219:-2:Kerberos Change Password Service:/var/empty:/usr/bin/false
_devicemgr:*:220:220:Device Management Server:/var/empty:/usr/bin/false
_webauthserver:*:221:221:Web Auth Server:/var/empty:/usr/bin/false
_netbios:*:222:222:NetBIOS:/var/empty:/usr/bin/false
_warmd:*:224:224:Warm Daemon:/var/empty:/usr/bin/false
_dovenull:*:227:227:Dovecot Authentication:/var/empty:/usr/bin/false
_netstatistics:*:228:228:Network Statistics Daemon:/var/empty:/usr/bin/false
_avbdeviced:*:229:-2:Ethernet AVB Device Daemon:/var/empty:/usr/bin/false
_krb_krbtgt:*:230:-2:Open Directory Kerberos Ticket Granting Ticket:/var/empty:/usr/bin/false
_krb_kadmin:*:231:-2:Open Directory Kerberos Admin Service:/var/empty:/usr/bin/false
_krb_changepw:*:232:-2:Open Directory Kerberos Change Password Service:/var/empty:/usr/bin/false
_krb_kerberos:*:233:-2:Open Directory Kerberos:/var/empty:/usr/bin/false
_krb_anonymous:*:234:-2:Open Directory Kerberos Anonymous:/var/empty:/usr/bin/false
_assetcache:*:235:235:Asset Cache Service:/var/empty:/usr/bin/false
_coremediaiod:*:236:236:Core Media IO Daemon:/var/empty:/usr/bin/false
_launchservicesd:*:239:239:_launchservicesd:/var/empty:/usr/bin/false
_iconservices:*:240:240:IconServices:/var/empty:/usr/bin/false
_distnote:*:241:241:DistNote:/var/empty:/usr/bin/false
_nsurlsessiond:*:242:242:NSURLSession Daemon:/var/db/nsurlsessiond:/usr/bin/false
_displaypolicyd:*:244:244:Display Policy Daemon:/var/empty:/usr/bin/false
_astris:*:245:245:Astris Services:/var/db/astris:/usr/bin/false
_krbfast:*:246:-2:Kerberos FAST Account:/var/empty:/usr/bin/false
_gamecontrollerd:*:247:247:Game Controller Daemon:/var/empty:/usr/bin/false
_mbsetupuser:*:248:248:Setup User:/var/setup:/bin/bash
_ondemand:*:249:249:On Demand Resource Daemon:/var/db/ondemand:/usr/bin/false
_xserverdocs:*:251:251:macOS Server Documents Service:/var/empty:/usr/bin/false
_wwwproxy:*:252:252:WWW Proxy:/var/empty:/usr/bin/false
_mobileasset:*:253:253:MobileAsset User:/var/ma:/usr/bin/false
_findmydevice:*:254:254:Find My Device Daemon:/var/db/findmydevice:/usr/bin/false
_datadetectors:*:257:257:DataDetectors:/var/db/datadetectors:/usr/bin/false
_captiveagent:*:258:258:captiveagent:/var/empty:/usr/bin/false
_ctkd:*:259:259:ctkd Account:/var/empty:/usr/bin/false
_applepay:*:260:260:applepay Account:/var/db/applepay:/usr/bin/false
_hidd:*:261:261:HID Service User:/var/db/hidd:/usr/bin/false
_cmiodalassistants:*:262:262:CoreMedia IO Assistants User:/var/db/cmiodalassistants:/usr/bin/false
_analyticsd:*:263:263:Analytics Daemon:/var/db/analyticsd:/usr/bin/false
_fpsd:*:265:265:FPS Daemon:/var/db/fpsd:/usr/bin/false
_timed:*:266:266:Time Sync Daemon:/var/db/timed:/usr/bin/false
_nearbyd:*:268:268:Proximity and Ranging Daemon:/var/db/nearbyd:/usr/bin/false
_reportmemoryexception:*:269:269:ReportMemoryException:/var/db/reportmemoryexception:/usr/bin/false
_driverkit:*:270:270:DriverKit:/var/empty:/usr/bin/false
_diskimagesiod:*:271:271:DiskImages IO Daemon:/var/db/diskimagesiod:/usr/bin/false
_logd:*:272:272:Log Daemon:/var/db/diagnostics:/usr/bin/false
_appinstalld:*:273:273:App Install Daemon:/var/db/appinstalld:/usr/bin/false
_installcoordinationd:*:274:274:Install Coordination Daemon:/var/db/installcoordinationd:/usr/bin/false
_demod:*:275:275:Demo Daemon:/var/empty:/usr/bin/false
_rmd:*:277:277:Remote Management Daemon:/var/db/rmd:/usr/bin/false
_accessoryupdater:*:278:278:Accessory Update Daemon:/var/db/accessoryupdater:/usr/bin/false
_knowledgegraphd:*:279:279:Knowledge Graph Daemon:/var/db/knowledgegraphd:/usr/bin/false
_coreml:*:280:280:CoreML Services:/var/db/coreml:/usr/bin/false
_sntpd:*:281:281:SNTP Server Daemon:/var/empty:/usr/bin/false
_trustd:*:282:282:trustd:/var/empty:/usr/bin/false
_mmaintenanced:*:283:283:mmaintenanced:/var/db/mmaintenanced:/usr/bin/false
_darwindaemon:*:284:284:Darwin Daemon:/var/db/darwindaemon:/usr/bin/false
_notification_proxy:*:285:285:Notification Proxy:/var/empty:/usr/bin/false
_avphidbridge:*:288:288:Apple Virtual Platform HID Bridge:/var/empty:/usr/bin/false
_biome:*:289:289:Biome:/var/db/biome:/usr/bin/false
_backgroundassets:*:291:291:Background Assets Service:/var/empty:/usr/bin/false
_mobilegestalthelper:*:293:293:MobileGestaltHelper:/var/empty:/usr/bin/false
_audiomxd:*:294:294:Audio and MediaExperience Daemon:/var/db/audiomxd:/usr/bin/false
_terminusd:*:295:295:Terminus:/var/db/terminus:/usr/bin/false
_neuralengine:*:296:296:AppleNeuralEngine:/var/db/neuralengine:/usr/bin/false
_eligibilityd:*:297:297:OS Eligibility Daemon:/var/db/eligibilityd:/usr/bin/false
_systemstatusd:*:298:298:SystemStatus Services:/var/empty:/usr/bin/false
_aonsensed:*:300:300:Always On Sense Daemon:/var/db/aonsensed:/usr/bin/false
_modelmanagerd:*:301:301:Model Manager:/var/db/modelmanagerd:/usr/bin/false
_reportsystemmemory:*:302:302:ReportSystemMemory:/var/empty:/usr/bin/false
_swtransparencyd:*:303:303:Software Transparency Services:/var/db/swtransparencyd:/usr/bin/false
_naturallanguaged:*:304:304:Natural Language Services:/var/db/com.apple.naturallanguaged:/usr/bin/false
_oahd:*:441:441:OAH Daemon:/var/empty:/usr/bin/false

It pretty densely used in the part leading up to 300. There are gaps though. Here’s a plot of the user IDs in order, to show those gaps.

User IDs 200-400 are supposedly special, being what some obscure sysadminctl command’s --help describes as “role” accounts. An answer labeled as “Apple” on their support forum explains that role accounts are the indeed accounts used by programs.

Unanswered questions:

  1. Are user IDs 0-99 special?
  2. Why is there a gap from 100-199?
  3. Why is _oahd all the way out there at 441?

Anyway, Nix moved their user IDs to 351+.

My last post was about either Android itself surviving Android 15 edge-to-edge enforcement (for View dinosaurs) or Those times when you’re scrolling through all the photos of yourself at famous places or of yourself eating at restaurants with your friends and you see one that’s just the inside of a cluttered living room from many, many apartments ago that you barely recognize anymore, a picture that didn’t commemorate some special milestone or prove you had the shoes that were absolutely it that one summer, a picture that means nothing anyone else, a picture taken by a you who thought you’d say “Hi” to the person that you are now and to remind you of an evening when your work was done and your TV show would be on soon and you had ice cream in the freezer and there was nowhere else you wanted to be at that moment. Find out which.

Please do not write below this line.