I haven’t made a decent technology post in some time, let alone one about my beloved Linux. To rectify that travesty, this post comes at a time to end said drought and to share with my Linux friends how to accomplish the goal outlined by the title. I do often see a fair number of questions as to how to get a local repository setup, but the contexts always vary a little by virtue of distribution as well as delivery mechanism. The objective here is to get up and running with as little hassle as possible. Our target distribution will be RHEL/CentOS 7 with delivery facilitated via FTP.

Getting right to it, there are six key points we need to address:

  1. Configuration of the FTP server
  2. Location for the software packages that will compose the repository(-ies)
  3. Creation of the repository metadata
  4. Firewall configuration
  5. SELinux configuration
  6. Exposure

FTP Server

Both RHEL and CentOS will by default install vsftpd as the FTP server of choice. This can be installed during the package selection phase of Anaconda by first selecting the Infrastructure Server profile and then the FTP Server group. You can install several other groups as well, but we only focus on this one here. Please note that if you intend on using another FTP package, you’ll want to skip some parts of this tutorial since it’s assumed that you are going to use vsftpd. If during the installation process you fail to install this package, simply install it post-installation with yum:

yum install vsftpd

The nice thing about installing it from Anaconda is that the default vsftpd configuration file (/etc/vsftpd/vsftpd.conf) is geared toward a public anonymous context with maybe only some slight modifications being required. Removing all of the comments from the file for brevity, these are the options that are used on the server I’ve configured:

anonymous_enable=YES
local_enable=YES
write_enable=NO
local_umask=022
xferlog_enable=YES
connect_from_port_20=YES
xferlog_std_format=YES
listen=YES
listen_ipv6=NO
pam_service_name=vsftpd
tcp_wrappers=YES

If you have to make any changes to this file, be sure to restart the daemon after writing said changes:

systemctl restart vsftpd

File Location

The repository files will be kept in a custom location, not in /var/ftp/pub – the default landing directory for anonymous. For this example, the files will be stored in /opt/repos. This will make it easier if we want to have multiple repositories on the same server. In other words, we could have a directory for the base CentOS packages – copied from the resource DVD – and custom packages for your company under another directory. Hypothetically, this leaves us with the following directory structures:

/opt/repos/centos/7/dvd/packages
/opt/repos/company/packages

Finally, you’ll want to change the permissions for the /opt/repos directory and its contents:

chmod -R 755 /opt/repos

Create Repositories

Next you’ll want to populate your newly created directory structures with the packages that will comprise the repository. Keeping with our example directories, the first will need to be copied from the CentOS Resource DVD. This can be accomplished by mounting the ISO/DVD and copying everything out of the Packages directory in the root of the mount. If you have them stored somewhere else, you’ll need to get them onto the server by other means (SCP, NFS, SMB, etc…). The same principle applies for the custom packages that you’ll be putting in the second directory. Ultimately, your storage and security strategy will dictate where the files are actually stored at and how they’re placed in those two aforementioned directories.

If you haven’t done so already, you’ll want to install the createrepo package. This package will automate the creation of the metafiles required for both identifying and advertising the manifest of a repository. Once you have the package installed, you’ll want to use it to create the repository for each of these directories. Createrepo takes a path as an argument. It also takes other options, but for this example, it’s satisfactory enough to omit them and provide only the directory. When you do this, do not inlcude the packages portion of the path. Instead, you’ll provide the path up to that point. Obviously, your current working directory will determine what you have to provide to createrepo. It’ll most likely look like one of the following forms:

createrepo /opt/repos/centos7/dvd
createrepo .
createrepo ../

Use whichever one you want, so long as the path is correct. The larger the number of packages createrepo has to parse, the longer it’ll take to process. As you might notice, parsing all of the CentOS Resource DVD packages will take some time (there’s almost 10,000 packages).

When you create the repositories in this manner, you’re essentially creating a static repository. If any of the packages in there change, you’ll need to issue a command to createrepo to update the repository manifest. Or you can make createrepo occasionally sync with a mirror, but these configurations are outside the immediate scope of this document.

Once the packages are in place and the repositories created, you’ll need to get them to the point of being exposed by the FTP server. Because the default public anonymous location for vsftpd is /var/ftp/pub, and because vsftpd doesn’t handle following symlinks very well (or not at all), you’ll want to use a bind mount to get the directory over there. The basic gist of a bind mount is to mount a portion of the filesystem to another portion of the filesystem. So if you perform a listing command on /var/ftp/pub prior to the bind mount, you’ll likely get nothing back since that directory doesn’t (or at least shouldn’t) contain anything after a fresh installation. If you perform a bind mount:

mount --bind /opt/repos /var/ftp/pub

and then list directory contents:

ls /var/ftp/pub

you’ll get returned two directories. Note that this doesn’t survive reboots unless you add the mount to fstab:

/opt/repos /var/ftp/pub xfs defaults,bind 0 0

If you don’t do this, don’t be shocked if after a reboot you can’t see anything on your FTP server since the mount will be disconnected.

Firewall Configuration

There’s a pretty good chance that your network interface is going to have the public zone from firewalld applied to it during the installation process. Even so, this zone likely won’t have the FTP server whitelisted, so you’ll need to check to see if it is and react accordingly.

First, check what name was given to the interface (henceforth referred to as ifname). Hopefully, it wasn’t given something unpredictable. You won’t have to do this if you explicitly name your interfaces during installation.

ip addr sh

Once you have the interface name, check to see which zone was applied to it through firewalld (henceforth referred to as zname):

firewall-cmd --get-zone-of-interface=ifname

Now, use this zone name to see what kinds of traffic are permitted or disallowed:

firewall-cmd --zone=zname --list-all

Most likely, if this is the default public zone, you’ll only see the services ssh and dhcpv6-client. The key here though is that if you don’t see ftp in the list of services, you’re going to need to add it.

firewall-cmd --permanent --zone=zname --add-service ftp

If during the initial configuration of vsftpd you elected to run FTP through a non-standard port, you’ll need to make the appropriate accommodations:

firewall-cmd --permanent --zone=zname --add-port port#/protocol

Once that’s done, reload firewalld rules:

firewall-cmd --reload

SELinux Configuration

At this point, you should be able to run an external port scan and see your FTP port open. However, it’s unlikely that you’re going to be able to access your files because of SELinux rules. Even though people hate it, and given too that this is a local server, you may be tempted to shut it off and go about your business. This post encourages that you leave it on and simply reconfigure it to work with your server.

Basically, you’ll need to change the SELinux type on the entire directory structure starting with the root /opt/repos to public_content_t.

chcon -R -t public_content_t /opt/repos

Testing and Exposure

Run a few simple tests before giving the green flag for clients to start consuming your packages. What I’ll usually do is run a port scan with nmap to verify that the FTP port is open, which effectively means that vsftpd is running and listening on that port. Next, I’ll open a browser and navigate to the address of the server with the FTP protocol to see if I can view the contents. You can also test this in two other ways:

  • Install a FTP client on the repository server and attempt to establish a FTP connection to localhost (I don’t recommend this for probably a foolish reason).
  • Use a FTP client on a remote client and attempt to establish a FTP connection to the repository server.

Two really common issues at this point are either access or visibility to the repository contents. If access is an issue, make sure that vsftpd is running on your server and that firewalld is configured to permit ingress/egress traffic for FTP, especially if you’re using a non-standard port for FTP (egress traffic should be open by default, but these require direct rules through firewall-cmd to filter since the principal route of focus for firewalld is ingress). If you’re still having issues, make sure that your clients are configured correctly too (firewall, routing, etc.). Visibility of content can usually be traced back to one of three matters: a bind mount that wasn’t added to fstab (this would cause the mount to be dismounted on restart), incorrect DAC (755 should be sufficient; FTP wants the execute bit set), or incorrect SELinux type. The only other major rub is that if your storage strategy defines that your files are located on a NAS or other file server, you need to ensure that those mounts are established at system start (i.e. remote SMB share is mounted correctly).

To add the repository to a client, you can either package the public data into a RPM and have clients install it (much the same way that RPM Fusion does theirs), or they can manually add it to the listing under /etc/yum.repos.d. The file would look similar to this:

[reponame]
name=Custom Repo
baseurl=ftp://name-or-ip-of-ftp-server/centos
gpgcheck=0

Helpful Links

VSFTPD Online Manpages
Firewalld Homepage
SELinux FTPD
Configuring a Yum Repository File

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