Slight correction, it does not look for a file named "d" in the home folder of the user in the (mistyped) -uid parameter, it looks for a file named "d" in the home folder of the user running sbatch. If this is not an expected behaviour, I will make a complete bug report.
On Tue, 9 Jul 2019 at 15:53, Daniel Torregrosa < daniel.torregr...@insight-centre.org> wrote: > Thanks a lot for your answers again! > > @Marcus Thanks a lot for the clarification. > > About --uid, you are correct, I was mistyping it as -uid. But, the > behaviour is slightly inconsistent: > * If correctly typed (--uid) sbatch properly complains about needing to be > root > * If not present at all, or ignored (by adding a non-commented line > before, like you said), everything goes fine > * If incorrectly typed (-uid UID), it silently fails UNLESS /home/UID/d > exists, then it is run as the requested user, i.e. if I add > > #SBATCH -uid test2 > > the log complains about /home/test2/d not existing. After creating that > file as test2 (that is, the file /home/test2/d is -rw-r--r-- test2:test2), > it executes the task as test (i.e. the output is, by default, in /home/test > and owned by test). I guess this is a bug? > > @Jeffrey Sorry, slurmdUser=sudo was a typo. Thanks a lot for the > clarifications regarding the POSIX capabilities. > > > On Tue, 9 Jul 2019 at 14:49, Jeffrey Frey <f...@udel.edu> wrote: > >> > So, if I understand this correctly, for some reason, `srun` does not >> need root privileges on the computation node side, but `sbatch` does when >> scheduling. I was afraid doing so would mean users could do things such as >> apt install and such, but it does not seem the case. >> >> The critical part here is slurmstepd running as one user (root, or slurm >> in your case) attempting to seteuid/setegid/setreuid/setregid the process. >> If not running as root, you'll see in the slurmstepd source code that the >> seteuid/setegid/setreuid/setregid calls are skipped -- thus, all job tasks >> run as SlurmdUser. On a multiuser system, SlurmdUser=root is necessary and >> safe. >> >> >> >> > I am not going to be managing the actual cluster, only exploring >> possibilities. At this point I am mostly convinced slurmdUser=sudo is safe, >> so that is one less potential problem. >> >> SlurmdUser must be set to a user name present on the machine. Setting it >> to "sudo" merely has it run as a user named "sudo." >> >> >> > @Patrick: I do not know how to do that. I only know that I can make >> slurm sudoer and NOPASSWD, but slurm would still call to `chown` (not `sudo >> chown`). An alternative would be replacing `chown` with a small script that >> calls `sudo chown`, but that is likely to break a lot of stuff. I assume >> slurmd will also need other root-only commands to work. >> >> The chown in question is a chown() system call in the slurmd/slurmstepd >> source code that's compiled into slurmd/slurmstepd. Replacing >> /usr/bin/chown with a custom command that calls sudo would not help at all >> (and would probably create a security issue). >> >> >> > @Michael Indeed, the documentation/tutorials often mention that >> SlurmdUser should be root, but it is not clearly explained why anywhere >> (e.g. https://slurm.schedmd.com/quickstart_admin.html section Daemons). >> It seems that `srun whoami` returns the current user (and not root), so >> even when slurmdUser is root, users do not have privileges, so in principle >> there is no problem at all. >> >> Again, the critical part here is slurmstepd's having the ability to >> change the running uid/gid of the processes it starts. With >> SlurmdUser=root, it can do this. With any other user name, it cannot, and >> every job step runs as SlurmdUser. >> >> >> >> > @Jeffrey It is expected to be multi-user. As for your third option, I >> think you refer to something similar to what I wrote for Patrick. >> >> I was talking about POSIX capabilities, and the possibility that all the >> capabilities exist to grant to slurmstepd the ability to chown() like root >> can, etc. That still doesn't help with the >> seteuid/setegid/setreuid/setregid calls because slurmstepd doesn't even >> make those calls when it's not running as root. >> >> >> >> >> :::::::::::::::::::::::::::::::::::::::::::::::::::::: >> Jeffrey T. Frey, Ph.D. >> Systems Programmer V / HPC Management >> Network & Systems Services / College of Engineering >> University of Delaware, Newark DE 19716 >> Office: (302) 831-6034 Mobile: (302) 419-4976 >> :::::::::::::::::::::::::::::::::::::::::::::::::::::: >> >> >> >> >> >>
