Ubuntu18.04的init程序合并到了systemd中，本篇文章记录一下systemd的下载和编译。

1. 下载systemd源码

(1) 查看systemd版本号，用来确定需要下载的分支

sun@sun-pc:~$ systemd --version
systemd 237
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid

(2) 上面看到systemd的版本是237，对应git仓库的v237 tag

sun@sun-pc:~/3rdcode$ git clone https://github.com/systemd/systemd.git --branch=v237

下载完成后，systemd目录内容如下：

sun@sun-pc:~/3rdcode/systemd$ ls
catalog       configure       ENVIRONMENT.md  hwdb             Makefile     meson_options.txt  modprobe.d  po       README.md  shell-completion  sysusers.d  TODO                   travis-ci     xorg
coccinelle    DISTRO_PORTING  factory         LICENSE.GPL2     man          mkosi.build        network     presets  rules      src               test        tools                  UIDS-GIDS.md
CODING_STYLE  docs            HACKING         LICENSE.LGPL2.1  meson.build  mkosi.default      NEWS        README   scripts    sysctl.d          tmpfiles.d  TRANSIENT-SETTINGS.md  units

2. 配置编译环境

systemd代码下载完成后，进入systemd目录，执行下面命令

sun@sun-pc:~/3rdcode/systemd$ ./configure 
+ exec meson build
The Meson build system
Version: 0.45.1
Source dir: /home/sun/3rdcode/systemd
Build dir: /home/sun/3rdcode/systemd/build
Build type: native build
...

配置完后，可以看到systemd目录多了一个build目录

sun@sun-pc:~/3rdcode/systemd$ ls
build       CODING_STYLE    docs            HACKING       LICENSE.LGPL2.1  meson.build        mkosi.default  NEWS     README     scripts           sysctl.d    tmpfiles.d  TRANSIENT-SETTINGS.md  units
catalog     configure       ENVIRONMENT.md  hwdb          Makefile         meson_options.txt  modprobe.d     po       README.md  shell-completion  sysusers.d  TODO        travis-ci              xorg
coccinelle  DISTRO_PORTING  factory         LICENSE.GPL2  man              mkosi.build        network        presets  rules      src               test        tools       UIDS-GIDS.md

3. 编译systemd源码

sun@sun-pc:~/3rdcode/systemd$ make