subogero linux blog

I’m always very proud how incredibly easily my Linux systems cooperate with the external world, including Windows machines.

For instance, just now, after one day of searching, sweating and swearing, I was able to mount some Windows shares onto a Debian virtual server.

For those of you who boast that one can do this with two clicks in Windows, let me tell you that

1. it’s actually 6 clicks
2. I also could have used Nautilus and just connect to a server

But that would have been too easy and, at the same time, too difficult to use. Have you ever seen such a Gnome gvfs mount point?

~/.gvfs/My bloody space-separated sharename on Foo

Brrrr. One wants something nice like

~/Foo

One also wants to be able to mount and unmount it as a normal user. And to have write access. And not having to enter a password, but also not to reveal it to others. One is very picky.

Before all, don’t forget to create the mount point directory manually. It shall be world-executable as well.

$ mkdir ~/Foo
$ chmod 775 ~/Foo

Now let’s see the /etc/fstab entry. We’ll explain every option later.

//srv/share /home/foo/Foo cifs rw,user,credentials=/home/foo/.foo,uid=1000,gid=1000 0 0

The entries are share UNC path, mount point, file system type, options, etc.

If you miss anything from the dreaded options, you’ll get the following highly informative error message when trying the mount:

mount error(13): Permission denied

Option “rw” means read-write. Easy.

Option “user” means not only root is allowed to mount or unmount the share.

Server “srv” is in domain “bar” and shares “share” for user “baz” whose password is “spam”. We could add these options directly to fstab (username=bar,password=spam,domain=baz), but that would make it world readable. Instead the info is stored in a credentials file in Linux user foo’s home. Make sure this file is readable by foo only. Let’s see its contents too:

$ chmod 600 ~/.foo
$ ls -l ~/.foo
-rw------- 1 foo foo size date .foo
$ cat ~/.foo
username=bar
domain=baz
password=spam

Don’t put any whitespace around the “=” signs. There is a school of thought that there should not be any character after the end of the password, not even a newline.

And last but not least, the Linux user’s user and group IDs should be specified as well. In our case “foo” is the first normal user on this machine, that’s why it’s 1000.

Now user foo should be able to mount and unmount the above share:

$ mount ~/Foo
$ umount ~/Foo

An OpenWrt router needs to be extended a bit to run big stuff. For instance to build a git-hub. The installed size of git is 91MB. One has an external USB HDD, of course, but what is the right way to do it? The forums are full of extroots and opts and similar stuff. I think they are all evil.

Extroot seems to involve compiling custom firmware images, while /opt brakes the nice Unixy directory structure (standard locations of programs, libs and daemons). There must be a better way:

Mount a partition of an external USB HDD to /usr

Just think about it. The really big files go to /usr/bin /usr/sbin and /usr/lib almost exclusively. Only small stuff goes to /etc, like config files and daemon startup scripts.

Today my theory was confirmed by practice. It’s very simple. These are the important steps:

1. Create an ext3 partition on your HDD just for this purpose

I actually did the partitioning before, on my normal Ubuntu laptop. It’s 2 GB and it’s called /dev/sda2 on the router.

2. Mount it to /opt temporarily

Create the /opt directory (or whatever else) temporarily and mount your partition into it using LUCI/Administration/System/Mount Points.

3. Copy the entire contents of /usr to /opt

The goal is that, initially, /usr looks the same with or without mounting something into it.

$ cp -dpr /usr/* /opt # preserve symlinks

4. Mount partition to /usr

Unmount /dev/sda2 from /opt, mount it into /usr using LUCI. You can also delete the temporary /opt directory.

5. Update /etc/opkg.conf

This involves OpenWrt’s most mysterious concept, overlay. Changing the line below has no effect except to calm down the worrying router about available storage-size for new packages:

option overlay_root /usr

You’re ready to install anything. As for me, I’ve since reinstalled mc and git. No dirty hacks this time with inserting /opt into PATH and manually creating some symlinks from /usr to /opt/usr. Just installed them like a breeze. My github is up and running again.