How to use busybox on Linux

BusyBox It's open source （GPL） project , Provide access to 400 A simple implementation of common commands .

It's easy to think that Linux Your orders are taken for granted . When you install Linux when , They are bundled with the system , And we often don't ask why they are there . Some basic commands , Such as  、  and echo, Not always a stand-alone application , It's actually built into your shell in . Other such as  、  and    It's the core toolkit （ Usually GNU coreutils） Part of . But in the open source world , There are always alternatives , The most interesting of all is  .

Linux Medium BusyBox brief introduction

BusyBox It's open source （GPL） project , Provide access to 400 A simple implementation of common commands , Include  ls、mv、ln、mkdir、more、ps、gzip、bzip2、tar  and  grep. It also includes programming languages  awk、 stream editor  sed、 File system checking tool  fsck、rpm  and  dpkg  Package manager , Of course, there is also a convenient way to access all these commands shell（sh）. In short , It contains all POSIX Basic commands required by the system , To perform common system maintenance tasks and many user and administrative tasks .

in fact , It even contains a  init  command , It can be used as PID 1 start-up , As the parent process of all other system services . let me put it another way ,BusyBox It can be used as  、OpenRC、sinit、init And other alternatives to initialization systems .

BusyBox A very small . As an executable , It's less than 1MB, So it's in  、  and    The field is very popular , Because the storage space of these scenes is very valuable . In the world of container and cloud computing , It serves as a streamlined Linux The basic image of container image is also very popular .

minimalism

BusyBox Part of its charm lies in its minimalism . All its commands are compiled into a binary file （busybox）, Its manual only 81 page （ According to my pair man Deliver to pr Calculation of pipeline ）, But it covers nearly 400 Bar command .

As an example of comparison , This is a “ original edition ” Of  useradd —help  Output ：

 -b, --base-dir BASE_DIR       base directory for home
 -c, --comment COMMENT         GECOS field of the new account
 -d, --home-dir HOME_DIR       home directory of the new account
 -D, --defaults                print or change the default config
 -e, --expiredate EXPIRE_DATE  expiration date of the new account
 -f, --inactive INACTIVE       password inactivity
 -g, --gid GROUP               name or ID of the primary group
 -G, --groups GROUPS           list of supplementary groups
 -h, --help                    display this help message and exit
 -k, --skel SKEL_DIR           alternative skeleton dir
 -K, --key KEY=VALUE           override /etc/login.defs
 -l, --no-log-init             do not add the user to the lastlog
 -m, --create-home             create the user's home directory
 -M, --no-create-home          do not create the user's home directory
 -N, --no-user-group           do not create a group with the user's name
 -o, --non-unique              allow users with non-unique UIDs
 -p, --password PASSWORD       encrypted password of the new account
 -r, --system                  create a system account
 -R, --root CHROOT_DIR         directory to chroot into
 -s, --shell SHELL             login shell of the new account
 -u, --uid UID                 user ID of the new account
 -U, --user-group              create a group with the same name as a user

And this is the same command BusyBox edition ：

 -h DIR    Home directory
 -g GECOS  GECOS field
 -s SHELL  Login shell
 -G GRP    Group
 -S            Create a system user
 -D            Don't assign a password
 -H            Don't create home directory
 -u UID    User id
 -k SKEL   Skeleton directory (/etc/skel)

Is this difference a feature or a limitation , It depends on whether you like your command to have 20 One option is still 10 An option . For some users and some use cases ,BusyBox Minimalism is just what you need . For others , It's a good minimization environment , It can be used as a backup tool , Or as a basis for installing more powerful tools , such as  、、GNU   wait .

install BusyBox

stay Linux On , You can use your package manager to install BusyBox. for example , stay Fedora And similar distributions ：

$ sudo dnf install busybox

stay Debian And its derivatives ：

$ sudo apt install busybox

stay MacOS On , have access to    or  . stay Windows On , have access to  .

You can take BusyBox Set to your shell, Use  chsh —shell  command , And then add BusyBox sh  The path to the application . I put BusyBox Put it in  /lib64  in , But its location depends on where your distribution is installed .

$ which busybox
/lib64/busybox/busybox
$ chsh --shell /lib64/busybox/sh

use BusyBox It's more complicated to completely replace all the common commands , Because most distributions are “ Hardwired ”, Will look for specific commands in specific software packages . let me put it another way , Although it can be used technically BusyBox Of  init  Replace the  init, But your package manager may refuse to let you delete the package that contains  init  Software package , Lest you worry that deleting will cause the system to fail to start . Some distributions are based on BusyBox Above , So starting from a new environment may be an experience BusyBox The simplest way to the system .

try BusyBox

You don't have to try BusyBox And put your shell Permanently changed to BusyBox. You can learn from your current shell Start one in BusyBox shell.

$ busybox sh
~ $

However, your system still has non installed BusyBox Version of command , So experience BusyBox Tools for , You must send the command as a parameter to  busybox  Executable file ：

~ $ busybox echo $0
sh
~ $ busybox ls --help
BusyBox vX.YY.Z (2021-08-25 07:31:48 NZST) multi-call binary.

Usage: ls [-1AaCxdLHRFplinshrSXvctu] [-w WIDTH] [FILE]...

List directory contents

 -1  One column output
 -a  Include entries that start with .
 -A  Like -a, but exclude . and ..
 -x  List by lines
[...]

In order to obtain “ complete ” Of BusyBox Experience , You can create one for each command  busybox  The symbolic link . This is easy. , As long as you use    Just go ：

$ mkdir bbx
$ for i in $(bbx --list); do \
    ln -s /path/to/busybox bbx/$i \
done

In your    Of   start   Add this symbolic link directory , And start the BusyBox：

$ PATH=$(pwd)/bbx:$PATH bbx/sh

To use

BusyBox It's an interesting project , It is also an achievable   The minimalist   An example of calculation . Whether you put BusyBox As     Lightweight environment , Or as    The user interface , Or try a new initialization system , Even for curiosity , Let yourself re recognize those familiar and unfamiliar commands , Will be very interesting .

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