## 20.1 Busybox

### 20.1.1 简介

下图直观地展示了本节内容：

![Busybox - Linux 瑞士军刀](../_images/busybox-logo.png)


`BusyBox` 是一个集成了一百多个最常用 Linux 命令和工具 (如 `cat`、`echo`、`grep`、`mount`、`telnet` 等) 的精简工具箱，它只需要几 MB 的大小，很方便进行各种快速验证，被誉为 “Linux 系统的瑞士军刀”。

`BusyBox` 可运行于多款 `POSIX` 环境的操作系统中，如 `Linux` (包括 `Android`)、`Hurd`、`FreeBSD` 等。

### 20.1.2 获取官方镜像

可以使用 `docker pull` 指令下载 `busybox:latest` 镜像：

```bash
$ docker pull busybox:latest
latest: Pulling from library/busybox
5c4213be9af9: Pull complete
Digest: sha256:c6b45a95f932202dbb27c31333c4789f45184a744060f6e569cc9d2bf1b9ad6f
Status: Downloaded newer image for busybox:latest
docker.io/library/busybox:latest
```
下载后，可以看到 `busybox` 镜像只有 **2.433 MB**：

```bash
$ docker image ls
REPOSITORY                   TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
busybox                   latest              e72ac664f4f0        6 weeks ago         2.433 MB
```

### 20.1.3 运行 busybox

启动一个 `busybox` 容器，并在容器中执行 `grep` 命令。

```bash
$ docker run -it busybox
/ # grep
BusyBox v1.22.1 (2014-05-22 23:22:11 UTC) multi-call binary.

Usage: grep [-HhnlLoqvsriwFE] [-m N] [-A/B/C N] PATTERN/-e PATTERN.../-f FILE [FILE]...

Search for PATTERN in FILEs (or stdin)

        -H      Add 'filename:' prefix
        -h      Do not add 'filename:' prefix
        -n      Add 'line_no:' prefix
        -l      Show only names of files that match
        -L      Show only names of files that don't match
        -c      Show only count of matching lines
        -o      Show only the matching part of line
        -q      Quiet. Return 0 if PATTERN is found, 1 otherwise
        -v      Select non-matching lines
        -s      Suppress open and read errors
        -r      Recurse
        -i      Ignore case
        -w      Match whole words only
        -x      Match whole lines only
        -F      PATTERN is a literal (not regexp)
        -E      PATTERN is an extended regexp
        -m N    Match up to N times per file
        -A N    Print N lines of trailing context
        -B N    Print N lines of leading context
        -C N    Same as '-A N -B N'
        -e PTRN Pattern to match
        -f FILE Read pattern from file
```
查看容器内的挂载信息。

```bash
/ # mount
overlay on / type overlay (rw,relatime,lowerdir=/var/lib/docker/overlay2/l/BOTCI5RF24AMC4A2UWF4N6ZWFP:/var/lib/docker/overlay2/l/TWVP5T5DMKJGXZOROR7CAPWGFP,upperdir=/var/lib/docker/overlay2/801ef0bf6cce35288dbb8fe00a4f9cc47760444693bfdf339ed0bdcf926e12a3/diff,workdir=/var/lib/docker/overlay2/801ef0bf6cce35288dbb8fe00a4f9cc47760444693bfdf339ed0bdcf926e12a3/work)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev type tmpfs (rw,nosuid,size=65536k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=666)
sysfs on /sys type sysfs (ro,nosuid,nodev,noexec,relatime)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,relatime,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (ro,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd)
cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (ro,nosuid,nodev,noexec,relatime,net_cls,net_prio)
cgroup on /sys/fs/cgroup/freezer type cgroup (ro,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (ro,nosuid,nodev,noexec,relatime,cpu,cpuacct)
cgroup on /sys/fs/cgroup/cpuset type cgroup (ro,nosuid,nodev,noexec,relatime,cpuset)
cgroup on /sys/fs/cgroup/blkio type cgroup (ro,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/perf_event type cgroup (ro,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/memory type cgroup (ro,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/devices type cgroup (ro,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/pids type cgroup (ro,nosuid,nodev,noexec,relatime,pids)
mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime)
shm on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=65536k)
/dev/vda1 on /etc/resolv.conf type ext3 (rw,noatime,data=ordered)
/dev/vda1 on /etc/hostname type ext3 (rw,noatime,data=ordered)
/dev/vda1 on /etc/hosts type ext3 (rw,noatime,data=ordered)
devpts on /dev/console type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=666)
proc on /proc/bus type proc (ro,relatime)
proc on /proc/fs type proc (ro,relatime)
proc on /proc/irq type proc (ro,relatime)
proc on /proc/sys type proc (ro,relatime)
proc on /proc/sysrq-trigger type proc (ro,relatime)
tmpfs on /proc/acpi type tmpfs (ro,relatime)
tmpfs on /proc/kcore type tmpfs (rw,nosuid,size=65536k,mode=755)
tmpfs on /proc/keys type tmpfs (rw,nosuid,size=65536k,mode=755)
tmpfs on /proc/timer_list type tmpfs (rw,nosuid,size=65536k,mode=755)
tmpfs on /proc/sched_debug type tmpfs (rw,nosuid,size=65536k,mode=755)
tmpfs on /sys/firmware type tmpfs (ro,relatime)
```
`busybox` 镜像虽然小巧，但包括了大量常见的 `Linux` 命令，读者可以用它快速熟悉 `Linux` 命令。

### 20.1.4 相关资源

* `Busybox` 官网：https://busybox.net/
* `Busybox` 官方仓库：https://git.busybox.net/busybox/
* `Busybox` 官方镜像：https://hub.docker.com/\_/busybox/
* `Busybox` 官方仓库：https://github.com/docker-library/busybox
