Overview
This post covers:
- How to examine files in an RPM package you possess
- How to examine files of an RPM package installed on a system
- How to extract a cpio archive from an RPM package
- How to extract files from a cpio archive
- How to show preinstall and postinstall scripts of an RPM package
- How to examine files in an RPM package in a remote repository
Extract files from an RPM (quick start)
For the impatient, this is the command to extract files from an RPM package you possess:
$ rpm2cpio ./packagecloud-test-1.1-1.x86_64.rpm | cpio -idmvContinue reading this post for more information about listing and extracting RPMs.
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What is an RPM package?
RPM stands for RedHat Package Manager and it is used in RedHat Linux and all its derivative Linuxes. RPM is also used to refer to the package format used to package software used by RedHatLinux and its derivates. An RPM package is simply a header structure on top of a CPIO archive. The package itself is comprised of four sections: a header with a leading identifier (magic number) that identifies the file as an RPM package, a signature to verify the integrity of the package, the header or ‘tagged’ data containing package information, version numbers, and copyright messaging, and the archive containing the actual program files.
How to list files in an RPM package file using the rpm command
The RPM package manager rpm comes with various utilities to interact with packages. The following command will list all the files inside an RPM package:
$ rpm -qlp ./path/to/test.rpm For example:
$ rpm -qlpv ./packagecloud-test-1.1-1.x86_64.rpm
-rwxr-xr-x 1 root root 8286 Jul 16 2014 /usr/local/bin/packagecloud_hello
In this example, the rpm command is used with the flag -q to specify it as a query command, -l to list the files in the package, and -p so it knows to query the uninstalled package file. The -v flag (verbose) just provides additional information (permissions, owner, etc.) for the sake of this example. As we can see, the package installs an executable binary called packagecloud_hello into /usr/local/bin/.
How to list files of an installed RPM package
Use the rpm command with -q and -l flags to list the files from an installed RPM package:
$ rpm -ql packagecloud-test
NOTE the use of a package’s name in the previous command and not the path to a specific RPM package.
How to extract cpio archive from RPM packages
To extract files from an RPM package you must first extract a cpio archive from the package itself. RedHat provides a utility called rpm2cpio which does exactly that:
$ rpm2cpio ./packagecloud-test-1.1-1.x86_64.rpm
How to extract files from an RPM package’s cpio archive
The rpm2cpio command will output (to stdout) a cpio archive from the RPM package. To extract the package files we’ll use the output from rpm2cpio and then use the cpio command to extract and create the files we need.
For example:
$ rpm2cpio ./packagecloud-test-1.1-1.x86_64.rpm | cpio -idmv
./usr/local/bin/packagecloud_hello
17 blocks
The cpio command copies files to and from archives. In the example above, we use cpio with the -i flag to extract the files from the archive, -d to create the leading directories where needed, and -m to preserve the file modification times when creating files. The -v flag (verbose) is to list the files processed for the sake of this example.
The result of our previous example is the creation of a ./usr/ folder in our working directory containing the files from the RPM package packagecloud-test-1.1-1.x86_64.rpm.
$ file usr/local/bin/packagecloud_hello
usr/local/bin/packagecloud_hello: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=0x77fe4f2fa02ee973bf4d74867729e950fcde7107, not stripped
NOTE that simply extracting package files to the root directory does NOT properly install a package. Use the yum or rpm tools to correctly install RPM packages.
How to show RPM package preinstall and postinstall scripts
To show the scripts that will run when a package is installed or uninstalled from a system, use the --scripts flag when querying a package using rpm. The following command will show the scripts for an uninstalled package test-1.1-1.el6.x86_64.rpm:
$ rpm -qp --scripts ./packagecloud-test-1.1-1.x86_64.rpm
This will output something like:
preinstall scriptlet (using /bin/sh):
# Do something
postinstall scriptlet (using /bin/sh):
if [ $1 -eq 1 ] ; then
# Do another thing
fi
preuninstall scriptlet (using /bin/sh):
if [ $1 -eq 0 ] ; then
# Do something else
fi
postuninstall scriptlet (using /bin/sh):
# Do things here, too
To view the scriptlets of an already installed package, you can use the following syntax when using rpm
$ rpm -q --scripts <packagename>
How to view contents of RPM packages on remote repositories using repoquery
repoquery is provided by the yum-utils package, make sure it’s installed:
$ yum install yum-utils
The repoquery command is used to query information from Yum repositories installed on the system. By default, the repoquery command will download the Yum repo metadata and update the cache. To run repoquery entirely from the Yum cache, use the -C or --cache flag. To list the contents of a package, pass the --list flag to the repoquery command:
$ repoquery --list <packagename>
For example:
$ repoquery --list packagecloud-test
/usr/local/bin/packagecloud_hello
This can be useful when viewing the contents of packages that aren’t downloaded or installed on your the system. repoquery will only provide information on packages avaliable in the configured Yum repositories.
Conclusion
Understanding how packages interact with the systems they’re installed on can be helpful in day-to-day operations. By knowing that the RPM package is comprised of a cpio archive and header data, we can extract the information needed with already existing tools (rpm2cpio and cpio) and use the RPM toolchain to query, inspect, and view the contents of an RPM package.
