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I'm setting up a Linux application which interfaces with programs designed to talk to a serial port. What's strange is that while I can access the pty by symlink if I am the owner user (klipper), I can't if I'm not, even if the other user (octoprint) is in the pty's owning group.

For context, the symlink is at /tmp/printer and the pty is at /dev/pts/1. SELinux is not installed and mount options are tmpfs on /tmp type tmpfs (rw,nosuid,nodev)

$ ls -l /tmp/printer
lrwxrwxrwx 1 klipper klipper 10 Oct 19 21:30 /tmp/printer -> /dev/pts/1

$ ls -l /dev/pts/1
crw-rw---- 1 klipper tty 136, 1 Oct 19 22:41 /dev/pts/1

$ groups klipper
network tty uucp klipper

$ sudo -u octoprint picocom /tmp/printer
<...>
FATAL: cannot open /tmp/printer: Permission denied

$ sudo -u octoprint picocom /dev/pts/1
<...>
Terminal ready
Yet Another User
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1 Answers1

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I believe this is due to the sticky bit typically set on/tmp. If you look at the permissions on /tmp, you’ll see that the last bit is t which implies that accessing a symlink inside of /tmp is limited to the owner of it. Your solution could be creating the symlink at another location.

diametralpitch
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