> For the complete documentation index, see [llms.txt](https://pshizhsysu.gitbook.io/linux/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://pshizhsysu.gitbook.io/linux/iptables/kuo-5c55-target/log.md).

# LOG

## `-j LOG [options]`

内核会把匹配到该规则的包的信息打出来，打印出来的日志可以通过`dmesg`或`syslogd`看到，如果`level`是前四种，日志会。这是一个`Non-Terminating Target`

常用的`options`有

> \--log-level level

`level`的值有`emerg`、`alert`、`critical`、`error`、`warning`、`notice`、`info`和`debug`

> \--log-prefix prefix

在该条日志的前面添加前缀，方便从所有日志中查找

## 示例

* 打印出目的地址为`10.254.0.1`的包的信息

```
$ iptables -t filter -I output -d 10.254.0.1 -j LOG --log-level info --log-prefix "Found packet to 10.254.0.1: "
```

接下来我们从本机上ping一下`10.254.0.1`

```
$ ping 10.254.0.1 -c 1
```

然后查看日志

```
$ dmesg | grep 10.254.0.1
[21646.526139] Found packet to 10.254.0.1IN= OUT=ens33 SRC=192.168.2.104 DST=10.254.0.1 LEN=84 TOS=0x00 PREC=0x00 TTL=64 ID=60109 DF PROTO=ICMP TYPE=8 CODE=0 ID=33079 SEQ=1
```