svscan(8)

💖 svscan — the girl who never sleeps 💖

okay bestie, welcome to svscan(8) from the System Manager's Manual, and no this is not a drill, she is THE momager of your whole service directory 🌸

✨ NAME ✨

svscan — starts and monitors a collection of services 👑

🦋 SYNOPSIS 🦋

svscan [ directory ]

💅 DESCRIPTION 💅

okay so. svscan looks at the current directory and, for every single subdirectory in it, it starts up one supervise(8) process. that's it, that's the job. she's a manager, she's delegating 💁‍♀️

the limit? 1000 subdirectories. that's her ceiling. after that she's like "bestie I cannot" 😭

subdirectory names that start with dots? she skips those entirely. hidden girls stay hidden 🙈

also important, like actually important: supervise(8) must be in svscan's path. if it isn't, this whole thing does not work, periodt.

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okay now the cute part 🌈. svscan can optionally start a pair of supervise(8) processes — one for a subdirectory s, and one for s/log — with a pipe running between them 🎀. it does this when:

• the name s is at most 255 bytes long, and
• s/log exists

ngl, quick lore drop for the oldheads: in versions 0.70 and below, she did this if s was sticky. different vibe, same girl 💀

also she needs two free descriptors for each pipe, so keep an eye on that.

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every five seconds she does a little vibe check on the subdirectories again 🔥:

• sees a new subdirectory? she starts a new supervise(8) process ✨
• sees an old subdirectory where the supervise(8) process has exited? she restarts that supervise(8) process 💪
• in the log case, she reuses the same pipe so that no data is lost. iconic behaviour honestly.

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svscan is designed to run forever. like, forever forever. she is the main character and she does not exit 👑

if she has trouble creating a pipe, or trouble running supervise(8), she prints a message to stderr and then just… tries again five seconds later. no drama, no quitting, she just gets back up 🫶

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and if you hand her a command-line argument directory, she switches to that directory when she starts 📂. simple as that.

🌟 SEE ALSO 🌟

• supervise(8)
• svc(8)
• svok(8)
• svstat(8)
• svscanboot(8)
• readproctitle(8)
• fghack(8)
• pgrphack(8)
• multilog(8)
• tai64n(8)
• tai64nlocal(8)
• setuidgid(8)
• envuidgid(8)
• envdir(8)
• softlimit(8)
• setlock(8)

http://cr.yp.to/daemontools.html 🦋

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and that's the whole page bestie!! it's from the daemontools System Manager's Manual and the little footer at the bottom just says svscan(8) — she said her own name on the way out, queen behaviour 💖✨ no cap, go run her, she's literally built to never stop 🎀