Ubuntu Download Hash Check
Download File https://fancli.com/2xUJke
The SHA256SUMS file contains checksums for ___ the available images (you can check this by opening the file) where a checksum exists - development and beta versions sometimes do not generate new checksums for each release.
Depending on your platform, you may or may not need to download the public key used to authenticate the checksum file (Ubuntu and most variants come with the relevant keys pre-installed). The easiest way to find out if you need the key is to run the authentication command:
If you get no results (or any result other than that shown above) then the ISO file does not match the checksum. This could be because the ISO has been altered, or it downloaded incorrectly - either way you should download a fresh ISO from a known good source.
A checksum is a string of letters and numbers that is unique to a file, like afingerprint. Checksums are generated by different algorithms, with the two mostpopular being 1_____________________________ and the 2___ algorithm.Ubuntu MATE provides the 3______ checksum on its download page.
Verifying a download involves checking the checksum of the file you downloadedversus the checksum provided on the download web site. Mismatching checksumscan indicate a corrupted or otherwise compromised file, so verifying yourdownloads is a good habit to adopt!
I back up all my digital photos to a couple of places. I've been using the cp command, but--given the personal value--have started to wonder if there's a more reliable way. I'm no stranger to Linux, Bash, Perl, etc., so I could write something to copy and compare md5 hashes, but I was wondering if something already exists (reinvention, wheels and what-not).
Most of my googling for copy and (verify|valid|check|hash|confirm) turns up rsync. However, as far as I can tell, rsync only uses hashes to see if a file needs to be updated. It doesn't perform a hash comparison afterward.
ZFS has a benefit over RAID-5 in that it can detect and repair errors in the data stored on the individual discs, even if the drives do not report a read error while reading the data. It will detect, via checksums, that one of the discs returned corrupted information and will use the redundancy data to repair that disc.
Because of the way the checksumming in ZFS is designed, I felt that I could rely on it to store infrequently used data for long periods of time. Every week I run a "zpool scrub" which goes through and re-reads all the data and verifies checksums.
In the distant past, for a client, I implemented a database system that stored checksum information on all files stored under a particular directory. I then had another script that would run periodically and check the file against the checksum stored in the database. With that we could quickly detect a corrupted file and restore from backups. We were basically implementing the same sorts of checks that ZFS does internally.
Since v1.5.0, a selected source folder can be hashed, then copied & reconstructed to a destination folder where the content is again hashed for verification. Since 1.5.5, selected file masks can be used, too (*.doc; *.xls etc).
The arguments to stat will cause it to print the name of the file, followed by its octal permissions. The two finds will run one after the other, causing double the amount of disk IO, the first finding all file names and checksumming the contents, the second finding all file and directory names, printing name and mode. The list of "file names and checksums", followed by "names and directories, with permissions" will then be checksummed, for a smaller checksum.
It will just give you a hash of the ls output, that contains folders, sub-folders, their files, their timestamp, size and permissions. Pretty much everything that you would need to determine if something has changed.
However, that produces a slightly different hash than my sha256sum_dir bash function, which I present below, produces. So, to get the output hash to exactly match the output from my sha256sum_dir function, do this instead:
Assuming you just want to compare two directories for equality, you can use diff -r -q "dir1" "dir2" instead, which I wrapped in this diff_dir command. I learned about the diff command to compare entire folders here: how do I check that two folders are the same in linux.
Here is the output of my sha256sum_dir command on my ~/temp2 dir (which dir I describe just below so you can reproduce it and test this yourself). You can see the total folder hash is b86c66bcf2b033f65451e8c225425f315e618be961351992b7c7681c3822f6a3 in this case:
Here is the cmd and output of diff_dir to compare two dirs for equality. This is checking that copying an entire directory to my SD card just now worked correctly. I made the output indicate Directories match! whenever that is the case!:
I tried the most-upvoted answer here, and it doesn't work quite right as-is. It needs a little tweaking. It doesn't work quite right because the hash changes based on the folder-of-interest's base path! That means that an identical copy of some folder will have a different hash than the folder it was copied from even if the two folders are perfect matches and contain exactly the same content! That kind of defeats the purpose of taking a hash of the folder if the hashes of two identical folders differ! Let me explain:
If you then pipe that output string above to sha256sum again, it hashes the file hashes with their full file paths, which is not what we want! The file hashes may match in a folder and in a copy of that folder exactly, but the absolute paths do NOT match exactly, so they will produce different final hashes since we are hashing over the full file paths as part of our single, final hash!
Good. Now, if I hash that entire output string, since the file paths are all relative in it, the final hash will match exactly for a folder and its copy! In this way, we are hashing over the file contents and the file names within the directory of interest, to get a different hash for a given folder if either the file contents are different or the filenames are different, or both.
If you change the names of a file without changing their alphabetical order, the hash script will not detect it. But, if you change the order of the files or the contents of any file, running the script will give you a different hash than before.
So your only option here is to copy/paste the output from the previous command. With respect to why this wasn't working for you when you attempted it. This likely failed because when you use echo you introduced an additional character, a newline (\n) which altered the checksum string.
If you don't have the hash value file and just have the expected hash then you can just put the hash in a file with a space then star and the name of the file you're checking, or so it's like the expected output of the sha256sum command.
The chances are that you've seen references to hashes or checksums when you've downloaded software from the Internet. Often, the software will be displayed, and then near the link is a checksum. The checksum may be labeled as MD5, SHA, or with some other similar name. Here is an example using one of my favorite old games from the 1990s named Nethack:
Cryptography uses hashing to confirm that a file is unchanged. The simple explanation is that the same hashing method is used on a file at each end of an Internet download. The file is hashed on the web server by the web administrator, and the hash result is published. A user downloads the file and applies the same hash method. The hash results, or checksums, are compared. If the checksum of the downloaded file is the same as that of the original file, then the two files are identical, and there have been no unexpected changes due to file corruption, man-in-the-middle attacks, etc.
Hashing is a one-way process. The hashed result cannot be reversed to expose the original data. The checksum is a string of output that is a set size. Technically, that means that hashing is not encryption because encryption is intended to be reversed (decrypted).
What's the difference between the message digest and secure hash algorithms? The difference is in the mathematics involved, but the two accomplish similar goals. Sysadmins might prefer one over the other, but for most purposes, they function similarly. They are not, however, interchangeable. A hash generated with MD5 on one end of the connection will not be useful if SHA256 is used on the other end. The same hash method must be used on both sides.
SHA256 generates a bigger hash, and may take more time and computing power to complete. It is considered to be a more secure approach. MD5 is probably good enough for most basic integrity checks, such as file downloads.
Linux uses hashes in many places and situations. Checksums can be generated manually by the user. You'll see exactly how to do that later in the article. In addition, hash capabilities are included with /etc/shadow, rsync, and other utilities.
For example, the passwords stored in the /etc/shadow file are actually hashes. When you sign in to a Linux system, the authentication process compares the stored hash value against a hashed version of the password you typed in. If the two checksums are identical, then the original password and what you typed in are identical. In other words, you entered the correct password. This is determined, however, without ever actually decrypting the stored password on your system. Check the first two characters of the second field for your user account in /etc/shadow. If the two characters are 4__, your password is encrypted with MD5. If the characters are 5__, your password is encrypted with SHA256. If the value is 6__, SHA512 is being used. SHA512 is used on my Fedora 33 virtual machine, as seen below:
Using the hash utilities is very simple. I will walk you through a very easy scenario to accomplish on a lab computer or whatever Linux system you have available. The purpose of this scenario is to determine whether a file has changed. 5376163bf9
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