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yajudge_grader

README.md

Grader Service for Yajudge

Prerequirements

  • Modern Linux Kernel and systemd-based distribution
  • cgroup v2 enabled by default in Linux system (see notes below)
  • Dart 2.12 or later
  • protoc compiler

NOTE: It is highly recommended to run grader service on Linux. It can run on macOS or some another POSIX-like system, but in this case all security-related features of grading system will be not available.

Build

Just type make from parent directory, or from this directory after package yajudge_common built.

In order to install type make install as root user to make installations into /usr system prefix.

System Configuration

Only recent (by Feb, 2022) Linux distributions have enabled by default cgroup version 2 but not 1.

Grader will not work in case of using legacy cgroup Linux subsystem. To enable cgroup v2 add the following parameters to the kernel command line:

systemd.unified_cgroup_hierarchy=1 cgroup_no_v1=all

On x86(-64) systems kernel parameters are set up by GRUB, so edit file /etc/default/grub:

GRUB_CMDLINE_LINUX="systemd.unified_cgroup_hierarchy=1 cgroup_no_v1=all"

Then run update-grub and reboot your system to apply changes.

On ARM systems with U-Boot loader (like Raspberry Pi) the same kernel parameters stored in file /boot/cmdline.txt (Raspbian) or /boot/firmware/cmdline.txt (Ubuntu).

To check if your system configured to use cgroup v2 examine the following command output:

mount | grep cgroup

You should see exactly one line of mounted file system of type cgroup2 but not several cgroup file systems.

Grader Configuration

Place conf/grader.yaml to one of the following places:

  • $HOME/.config/yajudge/grader.yaml
  • /etc/yajudge/grader.yaml

You can also set custom config file path using -C command line option.

Chrooted Environment Setup

Submission grading assumes using of dedicated 'clean' Linux environment for each problem submission. So it requires minimal Linux filesystem with required developer tools installed in some directory that not contain any private data.

Such filesystem may be obtained by several ways:

  • Just download and upack mini root filesystem from Alpine Linux. Note that Alpine's provided libc library lacks some usable features like sanitizers support.
  • Use debootstrap tool to create Debian or Ubuntu local environment. This works not only on Debian or Ubuntu hosts but also on openSUSE.
  • Use yours own specific distribution tool.

After creating local environment use sudo chroot ... (Debian) or unshare -muifrp --wd=/ --root=... (Alpine) command to enter that environment and configure target system.

Grader Usage

Service management

  • yajudge-grader start - starts service in background using proper systemd slice
  • yajudge-grader stop - stops previously started service
  • yajudge-grader daemon - run service in foreground. Note that it must be running within configured dedicated cgroup slice, for example by starting via systemd-run --wait command, or to be in use while configuring systemd service.

Local submissions testing

  • yajudge-grader run -c COURSE -p PROBLEM FILES... - queues local submission of problem with id PROBLEM and course with data id COURSE. The rest of command arguments are local submission files. After queuing it will wait for grader response.