Will I lose data in recovery mode?

Recovery Mode will not delete any of your data merely by entering it (or merely by trying it).

It is NOT a "System Restore" or "System Reset". It's merely access to a root prompt so you can troubleshoot and fix problems yourself.

If you just enter recovery mode, and make no changes, nothing "bad" will happen. Simply type exit and press Enter to exit recovery mode.

Recovery mode allows you to make changes to your system using a terminal console, but you have to explicitly grant yourself read/write access to do that.

You obviously already know how to get to the "recovery mode" menu, but I'll list the steps for completeness (adapted from Ubuntu Recovery Mode Wiki)

1. Switch on your computer.

2. With BIOS, quickly press and hold the Shift key to get grub menu.

   With UEFI press the Escape key to get grub menu.

3. Select the line which starts with "Advanced options".

4. Select the line ending with "(recovery mode)"

5. Press Return and your machine will begin the boot process.

   The "recovery mode" menu with a number of options will be displayed.

   One of these options is "Drop to root shell prompt", and I believe this is the option you are asking about. (There are other options, but I will specifically talk about the "root" option).

6. Highlight "root Drop to root shell prompt" and press Enter.

   Even though you are logged into your system as root, you can not (yet) accidentally make any changes.

   This is because the root partition (the "parent" / directory on your system) is mounted read-only.

To make changes to your system must explicitly do the following:

7. Mount / as read/write using the following command:

   mount -o remount,rw /
   

   Next, if you have other partitions that you need to access (such as a separate partition for /home) use the following command:

   mount --all
   

   This will mount all filesystems mentioned in fstab.

   Now, if you make any changes you could damage your system if you are not careful!

I address the question that you added in your comment:

I mean if you enter recovery mode will it wipe the data (?)

In itself, it will not wipe any data — only if you explicitly ask it to.

Recovery mode in itself is just a simplified variant (actually, a subset) of the operating system: it starts up only the very core of the system, the bare minimum that can give you a chance to interact with the computer and try to fix any error that may be present.

A lot of features (even important ones) are not being enabled in recovery mode by default, so that a faulty subsystem has less chance to cause any instability or further crash.

You may still encounter data-loss — but not caused by merely entering recovery mode — in three ways:

1. One way is that the data loss has already occurred even before you are entering the recovery mode. Some errors that necessitate that you enter recovery mode, might have already caused the data loss.
   • An example could be some degree of failure of the internal disk.
2. Another way may be if you do something on the root shell console that causes data loss: like typing and executing such commands on the command line that you are unfamiliar with, and whose consequences are not clear to you.
   • For example, any disk- or partitions-related command is definitely not a good candidate to use on the command line in a trial-and-error fashion. One should first learn about such commands, for example, by reading tutorials about them on the net. You can even ask us on this site regarding using specific commands.
3. And lastly, I think we could highlight such features of the recovery mode that may be not entirely risk-free; in case you choose to use them:
   • "Try to make free space"
     • Probably not risky at all, but it's about deleting files, so technically it's still about throwing some files away — but not yours though: it probably throws away files from the cache and temporary directories, that are not needed any more. (Though admittedly I don't know much about it.)
   • "Check all filesystems"
     • If the filesystem checking utility (called fsck) is being run in read-only mode, then it should be fine.
     • But if it's run in such a mode where it attempts to fix disk errors, there may be a low chance that it might not succeed in fixing the disk, and may leave it in a bad state.

The lesson should be that one always needs to keep backups of important data, preferably on a separate device: at the minimum on some sort of memory card, or an external disk.

Not keeping a backup and always just hoping that you can get out of every emergency without any data lost, may slowly, but likely, lead to unpleasant surprises.

short answer: NO

Recovery mode is just like safe mode boot in windows. You boot up with just the very minimal resources and programs loaded so that you can debug and troubleshoot some OS or module issues and recover from that.

You can of course, destroy your OS by running commands without knowing what you are doing, but that you can do even in normal mode. Linux command line is powerful, and with great power comes great responsibility. So know what a command can and is supposed to do before executing it.