The No Hang Daemon
==================

`Nohang` is a highly flexible full-featured daemon for Linux which is able to correctly prevent out of memory conditions.

### What is the problem?

OOM killer doesn't prevent OOM conditions.

### Solution

Use of [earlyoom](https://github.com/rfjakob/earlyoom) or nohang, but nohang is more featured.

### Demo

[Video](https://youtu.be/DefJBaKD7C8): nohang prevents OOM after command `while true; do tail /dev/zero; done` has been executed.

### Features

- convenient configuration with a config file with well-commented parameters (38 parameters in config)
- `SIGKILL` and `SIGTERM` as signals that can be sent to the victim
- `zram` support (`mem_used_total` as trigger)
- desktop notifications of attempts to prevent OOM
- low memory notifications
- black, white, prefer, avoid lists via regex
- possibility of restarting processes via command like `systemctl restart something` if the process is selected as a victim
- possibility of decrease `oom_score_adj`
- prevention of killing innocent victim via `oom_score_min`, `min_delay_after_sigterm` and `min_delay_after_sigkill` parameters
- customizable intensity of monitoring

### An exaple of output

```
MemAvail: 2975 M, 50.6 % | SwapFree: 10758 M, 100.0 %
MemAvail: 2976 M, 50.6 % | SwapFree: 10758 M, 100.0 %
MemAvail:    0 M,  0.0 % | SwapFree: 10281 M,  95.6 %
MemAvail:    0 M,  0.0 % | SwapFree:  9918 M,  92.2 %
MemAvail:    0 M,  0.0 % | SwapFree:  8659 M,  80.5 %
MemAvail:    0 M,  0.0 % | SwapFree:  7235 M,  67.3 %
MemAvail:   19 M,  0.3 % | SwapFree:  6851 M,  63.7 %
MemAvail:    0 M,  0.0 % | SwapFree:  5780 M,  53.7 %
MemAvail:    0 M,  0.0 % | SwapFree:  5008 M,  46.6 %
MemAvail:    0 M,  0.0 % | SwapFree:  4199 M,  39.0 %
MemAvail:    0 M,  0.0 % | SwapFree:  3502 M,  32.6 %
MemAvail:    0 M,  0.0 % | SwapFree:  2929 M,  27.2 %
MemAvail:    0 M,  0.0 % | SwapFree:  2446 M,  22.7 %
MemAvail:    0 M,  0.0 % | SwapFree:  2093 M,  19.5 %
MemAvail:    0 M,  0.0 % | SwapFree:  1573 M,  14.6 %
MemAvail:    0 M,  0.0 % | SwapFree:  1320 M,  12.3 %
MemAvail:    0 M,  0.0 % | SwapFree:  1117 M,  10.4 %
MemAvail:    0 M,  0.0 % | SwapFree:   943 M,   8.8 %

2018-07-06 Fri 03:04:37
  MemAvailable (0 MiB, 0.0 %) < mem_min_sigterm (588 MiB, 10.0 %)
  SwapFree (943 MiB, 8.8 %) < swap_min_sigterm (1076 MiB, 10.0 %)
  Preventing OOM: trying to send the SIGTERM signal to tail,
  Pid: 14636, Badness: 777, VmRSS: 4446 MiB, VmSwap: 8510 MiB
  Success
MemAvail:  173 M,  2.9 % | SwapFree:  3363 M,  31.3 %
MemAvail: 4700 M, 80.0 % | SwapFree:  8986 M,  83.5 %
MemAvail: 4668 M, 79.4 % | SwapFree:  8997 M,  83.6 %
MemAvail: 4610 M, 78.5 % | SwapFree:  9024 M,  83.9 %
MemAvail: 4533 M, 77.2 % | SwapFree:  9037 M,  84.0 %

```

### Requirements

- Linux 3.14+
- Python 3.4+

### Memory and CPU usage

- VmRSS is about 12 MiB
- CPU usage depends on the level of available memory (the frequency of memory status checks increases as the amount of available memory decreases)

### Download
```bash
git clone https://github.com/hakavlad/nohang.git
cd nohang
```

### Installation and start for systemd users

```bash
sudo ./install.sh
```
### Purge

```bash
sudo ./purge.sh
```

### Command line options

```
./nohang --help
usage: nohang [-h] [-c CONFIG]

optional arguments:
  -h, --help            show this help message and exit
  -c CONFIG, --config CONFIG
                        path to the config file, default values:
                        ./nohang.conf, /etc/nohang/nohang.conf
```

### How to configure nohang

Default path to config after installation is `/etc/nohang/nohang.conf`. The config is well commented. Read config and edit values before the start of the program.  Execute `sudo systemctl restart nohang` for apply changes.

### Feedback

Please, create [issues](https://github.com/hakavlad/nohang/issues).