How to obtain the source code of commands in CentOS system

Take the source code of the ls command under 32-bit CentOS6.6 as an example. You can use the following method to download the source code:

1) Configure the source of the source code

In CentOS, the source configuration file is: /etc/yum.repos.d/CentOS-Base.repo. Modifying this file requires root permissions.

Open the file and view the contents of the file. On my machine, the contents of the file are as follows:

# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client.You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the 
# remarked out baseurl= line instead.
#
#

[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#released updates 
[updates]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

There are two variables in this file: releasever and basearch, which represent the release version and branch respectively. For example, on my machine, these two values ​​​​are 6 and i386 respectively. Note that releasever will not be subdivided into minor versions, that is, it will not be 6.6 or the like.

From the content of the file, we can know that the file has 5 sections in total, which means that there are 5 software sources for my machine, namely base, updates, extras, centosplus and contrib. Therefore, you only need to specify the source code of the following 5 software sources. Add the following content at the end of the file:

[base-src]
name=CentOS-$releasever - Base src
baseurl=http://vault.centos.org/6.6/os/Source/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

[updates-src]
name=CentOS-$releasever - Updates src-centos
baseurl=http://vault.centos.org/6.6/updates/Source/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

[extras-src]
name=CentOS-$releasever -Extras src-centos
baseurl=http://vault.centos.org/6.6/extras/Source/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

[centosplus-src]
name=CentOS-$releasever - Plus src-centos
baseurl=http://vault.centos.org/6.6/centosplus/Source/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

[contrib-src]
name=CentOS-$releasever - Contrib src-centos
baseurl=http://vault.centos.org/6.6/contrib/Soruce/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

Since different versions have different settings, their settings will be different. The method can be summarized as follows:

(1) The gpgkey is the same as the gpgkey of the section already in the file

(2) In order to confirm the existence and status of the file, you can open the website http://vault.centos.org/ to view the specific situation, and then fill in the details according to the specific situation

(3) When setting the baseurl, you need to set it according to the version of your own system. For example, my machine is CentOS-6.6. When setting, the relevant parameters are set to 6.6, that is, http://vault.centos. The subpath following org/ is 6.6.

The function of this file is to provide a source for downloading yum and related work. For example, when using yumdownloader (discussed below) to download the source code, the following actions will occur:

(1) Download the $baseurl/repodata/repomd.xml file. If the repomd.xml file is newer than the one in the system, update the corresponding repomd.xml in the system

(2) Download the corresponding source code rpm package in $baseurl/SPackages/.

2) Use the which command to view the location of the ls command, as follows:

which ls

# Output: /bin/ls

3) Use the rpm command to query the package to which the ls command belongs, as follows:

rpm -qf /bin/ls

# Output: coreutils-8.4-37.el6.i686

4) yumdownloader is a program that downloads RPM from the RPM source. You can use the yumdownloader command to install the source code, as follows:

yumdownloader --source coreutils-8.4-37.el6.i686

Note:

(1) If the yumdownloader command is not installed, you can use this command to install it: yum install yum-utils.

(2) The downloaded file is in the current directory. You can use the parameter --destdir to specify which directory to download to.

5) Use yumdownloader to download an installation package file rpm. You can use the following command to query the tar file in the rpm:

rpm -qpl coreutils-8.4-37.el6.src.rpm | grep tar

# Output: coreutils-8.4.tar.xz

6) Use the rpm2cpio command to convert the rpm package file into a cpio archive file, and then use the cpio command to copy and extract an archive file from the cpio archive file. The output is as follows:

rpm2cpio coreutils-8.4-37.el6.src.rpm | cpio -idv coreutils-8.4.tar.xz

# Output:

# coreutils-8.4.tar.xz

# 9561 blocks

cpio's man explanation is: cpio copies files into an archive

-i: Same as --extract, meaning to extract

-d: Same as --make-directories, creates a loading directory when necessary

-v: List file processing

7) Use the tar command to decompress the coreutils-8.4.tar.xz compressed package, as follows:

tar -xvf ./coreutils-8.4.tar.xz

At this point, the source code of the command is obtained.

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