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Restore conditional logic for MeowIce flags (#3647)

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Co-authored-by: EmilyxFox <48589793+EmilyxFox@users.noreply.github.com>
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Geoff Bourne
2025-09-05 15:57:46 -05:00
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docs/configuration/jvm-options.md
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# JVM Options
## Memory Limit
By default, the image declares an initial and maximum Java memory-heap limit of 1 GB. There are several ways to adjust the memory settings:
- `MEMORY`: "1G" by default, can be used to adjust both initial (`Xms`) and max (`Xmx`) memory heap settings of the JVM
- `INIT_MEMORY`: independently sets the initial heap size
- `MAX_MEMORY`: independently sets the max heap size
The values of all three are passed directly to the JVM and support format/units as `<size>[g|G|m|M|k|K]`.
!!! example "Using docker run"
```
-e MEMORY=2G
```
or to use init and max memory:
```
-e INIT_MEMORY=1G -e MAX_MEMORY=4G
```
!!! example "Using compose file"
```
environment:
MEMORY: 2G
```
or to use init and max memory:
```
environment:
INIT_MEMORY: 1G
MAX_MEMORY: 4G
```
To let the JVM calculate the heap size from the container declared memory limit, unset `MEMORY` with an empty value, such as `-e MEMORY=""`. By default, the JVM will use 25% of the container memory limit as the heap limit; however, as an example the following would tell the JVM to use 75% of the container limit of 4GB of memory:
!!! example "MaxRAMPercentage using compose file"
```
environment:
MEMORY: ""
JVM_XX_OPTS: "-XX:MaxRAMPercentage=75"
deploy:
resources:
limits:
memory: 4G
```
!!! important
The settings above only set the Java **heap** limits. Memory resource requests and limits on the overall container should also account for non-heap memory usage. An extra 25% is [a general best practice](https://dzone.com/articles/best-practices-java-memory-arguments-for-container).
## Extra JVM Options
General JVM options can be passed to the Minecraft Server invocation by passing a `JVM_OPTS`
environment variable. The JVM requires `-XX` options to precede `-X` options, so those can be declared in `JVM_XX_OPTS`. Both variables are space-delimited, raw JVM arguments.
```
docker run ... -e JVM_OPTS="-someJVMOption someJVMOptionValue" ...
```
**NOTE** When declaring `JVM_OPTS` in a compose file's `environment` section with list syntax, **do not** include the quotes:
```yaml
environment:
- EULA=true
- JVM_OPTS=-someJVMOption someJVMOptionValue
```
Using object syntax is recommended and more intuitive:
```yaml
environment:
EULA: "true"
JVM_OPTS: "-someJVMOption someJVMOptionValue"
# or
# JVM_OPTS: -someJVMOption someJVMOptionValue
```
As a shorthand for passing several system properties as `-D` arguments, you can instead pass a comma separated list of `name=value` or `name:value` pairs with `JVM_DD_OPTS`. (The colon syntax is provided for management platforms like Plesk that don't allow `=` inside a value.)
For example, instead of passing
```yaml
JVM_OPTS: -Dfml.queryResult=confirm -Dname=value
```
you can use
```yaml
JVM_DD_OPTS: fml.queryResult=confirm,name=value
```
## Enable Remote JMX for Profiling
To enable remote JMX, such as for profiling with VisualVM or JMC, set the environment variable `ENABLE_JMX` to "true", set `JMX_HOST` to the IP/host running the Docker container, and add a port forwarding of TCP port 7091, such as:
!!! example
With `docker run`
```
-e ENABLE_JMX=true -e JMX_HOST=$HOSTNAME -p 7091:7091
```
If needing to map to a different port, then also set the environment variable `JMX_PORT` to the desired host port.
!!! example
With a compose file:
```yaml
environment:
ENABLE_JMX: true
JMX_HOST: ${HOSTNAME}
JMX_PORT: "7092"
ports:
- "7092:7092"
```
## Enable Aikar's Flags
[Aikar has done some research](https://aikar.co/2018/07/02/tuning-the-jvm-g1gc-garbage-collector-flags-for-minecraft/) into finding the optimal JVM flags for GC tuning, which becomes more important as more users are connected concurrently. [PaperMC also has an explanation](https://docs.papermc.io/paper/aikars-flags) of what the JVM flags are doing.
The set of flags documented there can be added using
-e USE_AIKAR_FLAGS=true
When `MEMORY` is greater than or equal to 12G, then the Aikar flags will be adjusted according to the article.
## Enable MeowIce's Flags
[MeowIce has created an updated set of JVM flags](https://github.com/MeowIce/meowice-flags?tab=readme-ov-file#why-would-i-have-to-switch-) based on Aikar's flags but with support for optimizations for Java 17 and above
The set of flags documented there can be added using
-e USE_MEOWICE_FLAGS=true
There is an optional `USE_MEOWICE_GRAALVM_FLAGS` variable to enable GraalVM specific optimizations, defaults to `TRUE` if USE_MEOWICE_GRAALVM_FLAGS is `TRUE`
# JVM Options
## Memory Limit
By default, the image declares an initial and maximum Java memory-heap limit of 1 GB. There are several ways to adjust the memory settings:
- `MEMORY`: "1G" by default, can be used to adjust both initial (`Xms`) and max (`Xmx`) memory heap settings of the JVM
- `INIT_MEMORY`: independently sets the initial heap size
- `MAX_MEMORY`: independently sets the max heap size
The values of all three are passed directly to the JVM and support format/units as `<size>[g|G|m|M|k|K]`.
!!! example "Using docker run"
```
-e MEMORY=2G
```
or to use init and max memory:
```
-e INIT_MEMORY=1G -e MAX_MEMORY=4G
```
!!! example "Using compose file"
```
environment:
MEMORY: 2G
```
or to use init and max memory:
```
environment:
INIT_MEMORY: 1G
MAX_MEMORY: 4G
```
To let the JVM calculate the heap size from the container declared memory limit, unset `MEMORY` with an empty value, such as `-e MEMORY=""`. By default, the JVM will use 25% of the container memory limit as the heap limit; however, as an example the following would tell the JVM to use 75% of the container limit of 4GB of memory:
!!! example "MaxRAMPercentage using compose file"
```
environment:
MEMORY: ""
JVM_XX_OPTS: "-XX:MaxRAMPercentage=75"
deploy:
resources:
limits:
memory: 4G
```
!!! important
The settings above only set the Java **heap** limits. Memory resource requests and limits on the overall container should also account for non-heap memory usage. An extra 25% is [a general best practice](https://dzone.com/articles/best-practices-java-memory-arguments-for-container).
## Extra JVM Options
General JVM options can be passed to the Minecraft Server invocation by passing a `JVM_OPTS`
environment variable. The JVM requires `-XX` options to precede `-X` options, so those can be declared in `JVM_XX_OPTS`. Both variables are space-delimited, raw JVM arguments.
```
docker run ... -e JVM_OPTS="-someJVMOption someJVMOptionValue" ...
```
**NOTE** When declaring `JVM_OPTS` in a compose file's `environment` section with list syntax, **do not** include the quotes:
```yaml
environment:
- EULA=true
- JVM_OPTS=-someJVMOption someJVMOptionValue
```
Using object syntax is recommended and more intuitive:
```yaml
environment:
EULA: "true"
JVM_OPTS: "-someJVMOption someJVMOptionValue"
# or
# JVM_OPTS: -someJVMOption someJVMOptionValue
```
As a shorthand for passing several system properties as `-D` arguments, you can instead pass a comma separated list of `name=value` or `name:value` pairs with `JVM_DD_OPTS`. (The colon syntax is provided for management platforms like Plesk that don't allow `=` inside a value.)
For example, instead of passing
```yaml
JVM_OPTS: -Dfml.queryResult=confirm -Dname=value
```
you can use
```yaml
JVM_DD_OPTS: fml.queryResult=confirm,name=value
```
## Enable Remote JMX for Profiling
To enable remote JMX, such as for profiling with VisualVM or JMC, set the environment variable `ENABLE_JMX` to "true", set `JMX_HOST` to the IP/host running the Docker container, and add a port forwarding of TCP port 7091, such as:
!!! example
With `docker run`
```
-e ENABLE_JMX=true -e JMX_HOST=$HOSTNAME -p 7091:7091
```
If needing to map to a different port, then also set the environment variable `JMX_PORT` to the desired host port.
!!! example
With a compose file:
```yaml
environment:
ENABLE_JMX: true
JMX_HOST: ${HOSTNAME}
JMX_PORT: "7092"
ports:
- "7092:7092"
```
## Enable Aikar's Flags
[Aikar has done some research](https://aikar.co/2018/07/02/tuning-the-jvm-g1gc-garbage-collector-flags-for-minecraft/) into finding the optimal JVM flags for GC tuning, which becomes more important as more users are connected concurrently. [PaperMC also has an explanation](https://docs.papermc.io/paper/aikars-flags) of what the JVM flags are doing.
The set of flags documented there can be added using
-e USE_AIKAR_FLAGS=true
When `MEMORY` is greater than or equal to 12G, then the Aikar flags will be adjusted according to the article.
## Enable MeowIce's Flags
[MeowIce has created an updated set of JVM flags](https://github.com/MeowIce/meowice-flags?tab=readme-ov-file#why-would-i-have-to-switch-) based on Aikar's flags but with support for optimizations for Java 17 and above
The set of flags documented there can be added by setting the environment variable `USE_MEOWICE_FLAGS` to `true`. There is an optional `USE_MEOWICE_GRAALVM_FLAGS` variable to enable GraalVM specific optimizations, defaults to `FALSE`.