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What Is Odex And Deodex In Android [Complete Guide]

As an Android newbie, what bothered me most was coming across terminology beyond my comprehension. Not coming from a Linux background it became hard to keep up with the oh-so-commonly-used words spread all across the development community. Likewise, since I didn’t understand the terms, consequently I was unable to determine is something was of any use to me or not. From what I have seen, this problem extends to many novice and even average users.

One commonly occurring word when playing with custom ROMs and firmware, and even themes is deodexed and odexed. Most users fail to understand what these terms actually imply, and while developers would boast again and again about their themes and ROMs being deodexed, the average user is left clueless as to what is going on.

In this article, we’ll try to explain what odexed and deodexed means, and what implications does it bring to a casual user.

WHAT IS AN ODEX FILE?

In Android file system, applications come in packages with the extension .apk. These application packages, or APKs contain certain .odex files whose supposed function is to save space. These ‘odex’ files are actually collections of parts of an application that are optimized before booting. Doing so speeds up the boot process, as it preloads part of an application. On the other hand, it also makes hacking those applications difficult because a part of the coding has already been extracted to another location before execution.

THEN COMES DEODEX

Deodexing is basically repackaging of these APKs in a certain way, such that they are reassembled into classes.dex files. By doing that, all pieces of an application package are put together back in one place, thus eliminating the worry of a modified APK conflicting with some separate odexed parts.

In summary, Deodexed ROMs (or APKs) have all their application packages put back together in one place, allowing for easy modification such as theming. Since no pieces of code are coming from any external location, custom ROMs or APKs are always deodexed to ensure integrity.

HOW THIS WORKS

For the more geeky amongst us, Android OS uses a Java-based virtual machine for running applications, called the Dalvik Virtual Machine. A deodexed, or .dex file contains the cache used by this virtual machine (referred to as Dalvik-cache) for a program, and it is stored inside the APK. An .odex file, on the other hand, is an optimized version of this same .dex file that is stored next to the APK as opposed to inside it. Android applies this technique by default to all the system applications.

Now, when an Android-based system is booting, the davlik cache for the Davlik VM is built using these .odex files, allowing the OS to learn in advance what applications will be loaded, and thus speeds up the booting process.

By deodexing these APKs, a developer actually puts the .odex files back inside their respective APK packages. Since all code is now contained within the APK itself, it becomes possible to modify any application package without conflicting with the operating system’s execution environment.

ADVANTAGES & DISADVANTAGES

The advantage of deodexing is in modification possibilities. This is most widely used in custom ROMs and themes. A developer building a custom ROM would almost always choose to deodex the ROM package first, since that would not only allow him to modify various APKs, but also leave room for post-install theming.

On the other hand, since the .odex files were supposed to quickly build the dalvik cache, removing them would mean longer initial boot times. However, this is true only for the first ever boot after deodexing, since the cache would still get built over time as applications are used. Longer boot times may only be seen again if the dalvik cache is wiped for some reason.

For a casual user, the main implication is in theming possibilities. Themes for android come in APKs too, and if you want to modify any of those, you should always choose a dedoexed custom ROM.

Was this article helpful? If you are confused with some other terms and want us to help explain them, please let us know in the comments.

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88 Comments

  2. Sad how I’m currently in college for Cyber Security and am just now learning about the technical stuff like ODEX and DECODEX.

  5. I like the post but I have little doubt about its correctness. Anyway, it is useful and thanks to author..

  6. The link to the deodexed ROM zip is no longer available. Was redirected to a spam download.

  8. hats off for you guys !! and that was awesome .. now I understand how custom ROMs are built .. and I’m gonna try to build my own ROM

  10. i have changed framework.odex file then it gives me “stale dependancy error ” plz let me know if you have any solution of this error….”Thanks “

  18. I come from a Linux background – we don’t use most of the terminology you find in the phone modding community. The phone modding community is its own special type of animal only distantly related to the Linux community.

  22. Is this an OS feature? I mean if you have to specify to your application that it is possible to build this files. And, in my device, the odex for the google play (vending) is not created, is this fact application design based or os based?

  24. Thank you. I always wondered what that meant. Now as I was reading this, I was wondering if I would ever be faced with a scenario where I had to install a deodexed apk on a odexed Rom, or vise versa. Would there be any issues? Would it even work? Would I even have to worry about such a scenario? Thanks in advance for the info!

  25. Very helpful! Thanks! I’m an advanced windows user and a novice linux user so a lot of it could be very confusing but I keep catching up thanks to articles like yours.

  33. As I understandDalvik VM preloads part of Application, and builds Dalvik cache, from odex file.
    Then maybe without odex, Dalvik VM builds cache by extracting portion of apk file.
    Is it right?

    Then odex just help Dalvik VM build Dalvik cache faster. Then booting will be faster.

    Dalvik VM speeds up the application lunching.

    Is it right?

  34. In post, odex speed up the boot proces..

    What boot?

    A system boot process, just when you turn on the device?

    Or a application boot process, when every time you lunching the apps?

  38. I know this is old, but I still send this link to someone when they ask me about odex and deodex. deserves a bump.

  39. THANKS!!! please keep understanding and sharing how does android work, there is almost no clear info about this around internet.

  41. Thanks so much for that explanation…it’s all starting to come into focus now!! 🙂

    • HW encoding is where the CPU does the encoding, SW encoding is where the encoding program does the encoding (also applies for decoding)

  44. Rubbish article.Information is scattered , and the issue doesn’t seem that hard to explain.maybe some drawings will help understanding.

    • Did you notice that most everyone found the article clear and helpful? Perhaps you would benefit from some reading and comprehension skills training along with some thoughts on civility in you responses. AND you may be a visual learner which still doesn’t excuse you disparaging remark.

  45. Only place in the web that provides a full (clear) explanation about this subject.
    Thanks!

  46. does this mean that I could delete all my .odex files and other than a first, longer boot my android would run ok afterwards?

    • No, you could not just delete your .odex files, you would need to repackage them as a “classes.dex” file then put that classes.dex file into the apk. You would have to do this for all system applications. If you were to just delete the odex all your apps would stop working.

  51. thanks for the post have been breaking my head from long time on this 🙂
     

  66. Thanks mate. It’s a valuable article.
    What did you mean by “odexed are Optimized”? optimized in terms of performance or memory?

  69. Love the way you explained it.. this would enable users (like me) choose among different custom roms and get exactly wat they want!!
    Thank a tonn..

  70. Thanks a lot for the clear explanation, I was scratching my head before reading this.

  72. Very helpful explaination. The question I have then is, when installing apps from the Market, Amazon, Handango or just side loading an APK downloaded from a forum or the like, are they odex or deodex? Will they sometimes be one and sometimes be the other? How would we know and how will they interact with whichever version of ROM we have? Will odex APKs cause problems on a deodex ROM and vis versa?

    • Did you ever find out the answer to these questions? I’d also like to know if “normal” .apk files will cause problems with Deodexed ROMs…

    • Side loaded and market apks are user apps, not system apps. This does not apply for them

    • What about when I want to integrate one app that I downloaded from Play store into a deodexed rom? Is this a problem? If it is, how can this be done?

    • how does converting a user app into a system app affect this? afterall, we got root…so surely installing as root user could make the apk ‘system-privilidged’, so to say…

  75. Thanks for breaking it down in an understandable and intuitive way. It really made a lot of sense and I for one am truly grateful.

    • Wow, Joel. You actually posted a link to your own article and said you “found” more information there? I fell for it and checked out that horrifyingly written article that was almost impossible to comprehend. My head hurts.

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