# View and restart Amazon EMR and application processes (daemons)
When you troubleshoot a cluster, you may want to list running processes. You may also want to stop or restart processesS. For example, you can restart a process after you change a configuration or notice a problem with a particular process after you analyze log files and error messages.
There are two types of processes that run on a cluster: Amazon EMR processes (for example, instance-controller and Log Pusher), and processes associated with the applications installed on the cluster (for example, hadoop-hdfs-namenode, and hadoop-yarn-resourcemanager).
To work with processes directly on a cluster, you must first connect to the master node. For more information, see [Connect to an Amazon EMR cluster](emr-connect-master-node.md).
## Viewing running processes
The method you use to view running processes on a cluster differs according to the Amazon EMR version you use.
------
#### [ EMR 5.30.0 and 6.0.0 and later ]
**Example : List all running processes**
The following example uses `systemctl` and specifies `--type` to view all processes.
```
systemctl --type=service
```
**Example : List specific processes**
The following example lists all processes with names that contain `hadoop`.
```
systemctl --type=service | grep -i {{hadoop}}
```
Example output:
```
hadoop-hdfs-namenode.service loaded active running Hadoop namenode
hadoop-httpfs.service loaded active running Hadoop httpfs
hadoop-kms.service loaded active running Hadoop kms
hadoop-mapreduce-historyserver.service loaded active running Hadoop historyserver
hadoop-state-pusher.service loaded active running Daemon process that processes and serves EMR metrics data.
hadoop-yarn-proxyserver.service loaded active running Hadoop proxyserver
hadoop-yarn-resourcemanager.service loaded active running Hadoop resourcemanager
hadoop-yarn-timelineserver.service loaded active running Hadoop timelineserver
```
**Example : See a detailed status report for a specific process**
The following example displays a detailed status report for the `hadoop-hdfs-namenode` service.
```
sudo systemctl status {{hadoop-hdfs-namenode}}
```
Example output:
```
hadoop-hdfs-namenode.service - Hadoop namenode
Loaded: loaded (/etc/systemd/system/hadoop-hdfs-namenode.service; enabled; vendor preset: disabled)
Active: active (running) since Wed 2021-08-18 21:01:46 UTC; 26min ago
Main PID: 9733 (java)
Tasks: 0
Memory: 1.1M
CGroup: /system.slice/hadoop-hdfs-namenode.service
‣ 9733 /etc/alternatives/jre/bin/java -Dproc_namenode -Xmx1843m -server -XX:OnOutOfMemoryError=kill -9 %p ...
Aug 18 21:01:37 ip-172-31-20-123 systemd[1]: Starting Hadoop namenode...
Aug 18 21:01:37 ip-172-31-20-123 su[9715]: (to hdfs) root on none
Aug 18 21:01:37 ip-172-31-20-123 hadoop-hdfs-namenode[9683]: starting namenode, logging to /var/log/hadoop-hdfs/ha...out
Aug 18 21:01:46 ip-172-31-20-123 hadoop-hdfs-namenode[9683]: Started Hadoop namenode:[ OK ]
Aug 18 21:01:46 ip-172-31-20-123 systemd[1]: Started Hadoop namenode.
Hint: Some lines were ellipsized, use -l to show in full.
```
------
#### [ EMR 4.x - 5.29.0 ]
**Example : List all running processes**
The following example lists all running processes.
```
initctl list
```
------
#### [ EMR 2.x - 3.x ]
**Example : List all running processes**
The following example lists all running processes.
```
ls /etc/init.d/
```
------
## Stopping and restarting processes
After you determine which processes are running, you can stop and then restart them if necessary.
------
#### [ EMR 5.30.0 and 6.0.0 and later ]
**Example : Stop a process**
The following example stops the `hadoop-hdfs-namenode` process.
```
sudo systemctl stop {{hadoop-hdfs-namenode}}
```
You can query the `status` to verify that the process is stopped.
```
sudo systemctl status {{hadoop-hdfs-namenode}}
```
Example output:
```
hadoop-hdfs-namenode.service - Hadoop namenode
Loaded: loaded (/etc/systemd/system/hadoop-hdfs-namenode.service; enabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Wed 2021-08-18 21:37:50 UTC; 8s ago
Main PID: 9733 (code=exited, status=143)
```
**Example : Start a process**
The following example starts the `hadoop-hdfs-namenode` process.
```
sudo systemctl start {{hadoop-hdfs-namenode}}
```
You can query the status to verify that the process is running.
```
sudo systemctl status {{hadoop-hdfs-namenode}}
```
Example output:
```
hadoop-hdfs-namenode.service - Hadoop namenode
Loaded: loaded (/etc/systemd/system/hadoop-hdfs-namenode.service; enabled; vendor preset: disabled)
Active: active (running) since Wed 2021-08-18 21:38:24 UTC; 2s ago
Process: 13748 ExecStart=/etc/init.d/hadoop-hdfs-namenode start (code=exited, status=0/SUCCESS)
Main PID: 13800 (java)
Tasks: 0
Memory: 1.1M
CGroup: /system.slice/hadoop-hdfs-namenode.service
‣ 13800 /etc/alternatives/jre/bin/java -Dproc_namenode -Xmx1843m -server -XX:OnOutOfMemoryError=kill -9 %p...
```
------
#### [ EMR 4.x - 5.29.0 ]
**Example : Stop a running process**
The following example stops the `hadoop-hdfs-namenode` service.
```
sudo stop {{hadoop-hdfs-namenode}}
```
**Example : Restart a stopped process**
The following example restarts the `hadoop-hdfs-namenode` service. You must use the `start` command and not `restart`.
```
sudo start {{hadoop-hdfs-namenode}}
```
**Example : Check the process status**
The following fetches the status for `hadoop-hdfs-namenode`. You can use the `status` command to verify that the process has stopped or started.
```
sudo status {{hadoop-hdfs-namenode}}
```
------
#### [ EMR 2.x - 3.x ]
**Example : Stop an application process**
The following example stops the `hadoop-hdfs-namenode` service, which is associated with the version of Amazon EMR installed on the cluster.
```
sudo /etc/init.d/{{hadoop-hdfs-namenode}} stop
```
**Example : Restart an application process**
The following example command restarts the `hadoop-hdfs-namenode` process:
```
sudo /etc/init.d/{{hadoop-hdfs-namenode}} start
```
**Example : Stop an Amazon EMR process**
The following example stops a process, such as instance-controller, which is not associated with the version of Amazon EMR on the cluster.
```
sudo /sbin/stop {{instance-controller}}
```
**Example : Restart an Amazon EMR process**
The following example restarts a process, such as instance-controller, which is not associated with the version of Amazon EMR on the cluster.
```
sudo /sbin/start {{instance-controller}}
```
**Note**
The `/sbin/start, stop` and `restart` commands are symlinks to `/sbin/intictl`. For more information about `initctl`, see the initctl man page by typing `man initctl` at the command prompt.
------