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# nats-top
## NATS TOP
[nats-top](https://github.com/nats-io/nats-top) is a [top](http://man7.org/linux/man-pages/man1/top.1.html)-like tool for monitoring nats-server servers.
The nats-top tool provides a dynamic real-time view of a NATS server. nats-top can display a variety of system summary information about the NATS server, such as subscription, pending bytes, number of messages, and more, in real time. For example:
```bash
nats-top
nats-server version 0.6.4 (uptime: 31m42s)
Server:
Load: CPU: 0.8% Memory: 5.9M Slow Consumers: 0
In: Msgs: 34.2K Bytes: 3.0M Msgs/Sec: 37.9 Bytes/Sec: 3389.7
Out: Msgs: 68.3K Bytes: 6.0M Msgs/Sec: 75.8 Bytes/Sec: 6779.4
Connections: 4
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION SUBSCRIPTIONS
127.0.0.1:56134 2 5 0 11.6K 11.6K 1.1M 905.1K go 1.1.0 foo, hello
127.0.1.1:56138 3 1 0 34.2K 0 3.0M 0 go 1.1.0 _INBOX.a96f3f6853616154d23d1b5072
127.0.0.1:56144 4 5 0 11.2K 11.1K 873.5K 1.1M go 1.1.0 foo, hello
127.0.0.1:56151 5 8 0 11.4K 11.5K 1014.6K 1.0M go 1.1.0 foo, hello
```
## Installation
nats-top can be installed using `go get`. For example:
```bash
go get github.com/nats-io/nats-top
```
NOTE: You may have to run the above command as user `sudo` depending on your setup. If you receive an error that you cannot install nats-top because your $GOPATH is not set, when in fact it is set, use command `sudo -E go get github.com/nats-io/nats-top` to install nats-top. The `-E` flag tells sudo to preserve the current user's environment.
## Usage
Once installed, nats-top can be run with the command `nats-top` and optional arguments.
```bash
nats-top [-s server] [-m monitor] [-n num_connections] [-d delay_in_secs] [-sort by]
```
## Options
Optional arguments inclde the following:
| Option | Description |
| :--- | :--- |
| `-m monitor` | Monitoring http port from nats-server. |
| `-n num_connections` | Limit the connections requested to the server \(default 1024\). |
| `-d delay_in_secs` | Screen refresh interval \(default 1 second\). |
| `-sort by` | Field to use for sorting the connections \(see below\). |
## Commands
While in nats-top view, you can use the following commands.
### option
Use the `o<option>` command to set the primary sort key to the `<option>` value. The option value can be one of the following: `cid`, `subs`, `pending`, `msgs_to`, `msgs_from`, `bytes_to`, `bytes_from`, `lang`, `version`.
You can also set the sort option on the command line using the `-sort` flag. For example: `nats-top -sort bytes_to`.
### limit
Use the `n<limit>` command to set the sample size of connections to request from the server.
You can also set this on the command line using the `-n num_connections` flag. For example: `nats-top -n 1`.
Note that if `n<limit>` is used in conjunction with `-sort`, the server will respect both options allowing queries such as the following: Query for the connection with largest number of subscriptions: `nats-top -n 1 -sort subs`.
### s, ? and q Commands
Use the `s` command to toggle displaying connection subscriptions.
Use the `?` command to show help message with options.
Use the `q` command to quit nats-top.
### Tutorial
For a walkthrough with `nats-top` check out the [tutorial](https://github.com/nats-io/nats.docs/tree/51fc56e3090645f7cedb242415e2d5361e1807e7/nats_tools/nats_top/tutorial.md).

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# Tutorial
You can use [nats-top](https://github.com/nats-io/nats-top) to monitor in realtime NATS server connections and message statistics.
## Prerequisites
* [Set up your Go environment](https://golang.org/doc/install)
* [Installed the NATS server](../../nats-server/installation.md)
## 1. Install nats-top
```bash
% go get github.com/nats-io/nats-top
```
You may need to run the following instead:
```bash
% sudo -E go get github.com/nats-io/nats-top
```
## 2. Start the NATS server with monitoring enabled
```bash
% nats-server -m 8222
```
## 3. Start nats-top
```bash
% nats-top
```
Result:
```bash
nats-server version 0.6.6 (uptime: 2m2s)
Server:
Load: CPU: 0.0% Memory: 6.3M Slow Consumers: 0
In: Msgs: 0 Bytes: 0 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 0 Bytes: 0 Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 0
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
```
## 4. Run NATS client programs
Run some NATS client programs and exchange messages.
For the best experience, you will want to run multiple subscribers, at least 2 or 3. Refer to the [example pub-sub clients](../../nats-server/clients.md).
## 5. Check nats-top for statistics
```bash
nats-server version 0.6.6 (uptime: 30m51s)
Server:
Load: CPU: 0.0% Memory: 10.3M Slow Consumers: 0
In: Msgs: 56 Bytes: 302 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 98 Bytes: 512 Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
::1:58651 6 1 0 52 0 260 0 go 1.1.0
::1:58922 38 1 0 21 0 105 0 go 1.1.0
::1:58953 39 1 0 21 0 105 0 go 1.1.0
```
## 6. Sort nats-top statistics
In nats-top, enter the command `o` followed by the option, such as `bytes_to`. You see that nats-top sorts the BYTES\_TO column in ascending order.
```bash
nats-server version 0.6.6 (uptime: 45m40s)
Server:
Load: CPU: 0.0% Memory: 10.4M Slow Consumers: 0
In: Msgs: 81 Bytes: 427 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 154 Bytes: 792 Msgs/Sec: 0.0 Bytes/Sec: 0
sort by [bytes_to]:
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
::1:59259 83 1 0 4 0 20 0 go 1.1.0
::1:59349 91 1 0 2 0 10 0 go 1.1.0
::1:59342 90 1 0 0 0 0 0 go 1.1.0
```
## 7. Use different sort options
Use some different sort options to explore nats-top, such as:
`cid`, `subs`, `pending`, `msgs_to`, `msgs_from`, `bytes_to`, `bytes_from`, `lang`, `version`
You can also set the sort option on the command line using the `-sort` flag. For example: `nats-top -sort bytes_to`.
## 8. Display the registered subscriptions.
In nats-top, enter the command `s` to toggle displaying connection subscriptions. When enabled, you see the subscription subject in nats-top table:
```bash
nats-server version 0.6.6 (uptime: 1h2m23s)
Server:
Load: CPU: 0.0% Memory: 10.4M Slow Consumers: 0
In: Msgs: 108 Bytes: 643 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 185 Bytes: 1.0K Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION SUBSCRIPTIONS
::1:59708 115 1 0 6 0 48 0 go 1.1.0 foo.bar
::1:59758 122 1 0 1 0 8 0 go 1.1.0 foo
::1:59817 124 1 0 0 0 0 0 go 1.1.0 foo
```
## 9. Quit nats-top
Use the `q` command to quit nats-top.
## 10. Restart nats-top with a specified query
For example, to query for the connection with largest number of subscriptions:
```bash
% nats-top -n 1 -sort subs
```
Result: nats-top displays only the client connection with the largest number of subscriptions:
```bash
nats-server version 0.6.6 (uptime: 1h7m0s)
Server:
Load: CPU: 0.0% Memory: 10.4M Slow Consumers: 0
In: Msgs: 109 Bytes: 651 Msgs/Sec: 0.0 Bytes/Sec: 0
Out: Msgs: 187 Bytes: 1.0K Msgs/Sec: 0.0 Bytes/Sec: 0
Connections: 3
HOST CID SUBS PENDING MSGS_TO MSGS_FROM BYTES_TO BYTES_FROM LANG VERSION
::1:59708 115 1 0 6 0 48 0 go 1.1.0
```