Linux Check 32 Bit 64 Bits
Josephine Heathershaw
Go to the System Settings and under the System section, hit Details. You will get every detail including your OS, your processor as well as the fact whether the system is running a 64-bit or a 32-bit version.
Open the Ubuntu Software Center and search for lib32. If that turns up any results, you are on a 64-bit install (the results are compatibility libraries for running 32-bit applications on a 64-bit install).
As far as I can remember, it is possible to install x86_64 kernel on a 32-bit system. As a few wrote here, you should look what libraries you have/what packages you have installed on your system. So the safest way to see is to check if you have /lib64 and if it is a symlink to /lib.
Another possible way is to check what packages you have downloaded in /var/cache/apt/archive. If they contain _amd64.deb, it is a 64-bit system, that is, if you have installed packages and have not cleared your cache.
Have a look at your Software Sources in Synaptic or Software Centre. If you haven't deleted your original source eg cdrom, it will (?) indicate the architecture. It's a GUI but it won't say '32bit' nor '64bit'.
Do you feel that my 32 bits environment should be called 32 bits (I believe so) or 64 bits (after all, it does run inside a 64 bits kernel). In that environment uname -m says i686 and all libraries and executables and processes are 32 bits.
How to find if a computer is running 32-bit or 64-bit operating system? If you want to install any new application on Linux or Ubuntu operating systems, It's better you check whether it is compatible with 32 bit or 64 bit OS to avoid any conflicts.
As I am using an Ubuntu system, so lets see how we can check on an Ubuntu server. I will show you different ways of checking whether your Ubuntu system is 32-bit or 64-bit. We will check both from shell and as well as from GUI.
64-bit processors have a data bus with 64-bit. It means they can handle at least twice the fast when compared to 32-bits. To meet the requirements with 64-bits processors, operating systems released their 64 bit versions.
VIRTIO devices have feature bits that indicate the presence of optional features. The feature bit space is divided into core VIRTIO features (e.g. notify on empty), transport-specific features (PCI, MMIO, CCW), and device-specific features (e.g. virtio-net checksum offloading). This article shows how to check whether a feature is enabled inside Linux guests.
The feature bits are used during VIRTIO device initialization to negotiate features between the device and the driver. The device reports a fixed set of features, typically all the features that the device implementors wanted to offer from the VIRTIO specification version that they developed against. The driver also reports features, typically all the features that the driver developers wanted to offer from the VIRTIO specification version that they developed against.
Feature bit negotiation determines the subset of features supported by both the device and the driver. A new driver might not be able to enable all the features it supports if the device is too old. The same is true vice versa. This offers compatibility between devices and drivers. It also means that you don't know which features are enabled until the device and driver have negotiated them at runtime.
The Linux virtio.ko driver that is used for all VIRTIO devices has a sysfs file called features. This file contains the feature bits in binary representation starting with the 1st bit on the left and more significant bits to the right. The reported bits are the subset that both the device and the driver support.
But those are oversimplifications and really comprehending the concepts well enough to pass an exam or use them effectively in the real world requires going a little deeper than that. Here, we're going to help you do just that. We'll review how setuid, setgid, and the sticky bit work and provide a list of common commands to help you get started. Having a strong understanding of these concepts is critical for passing any Linux certification.
Setuid and setgid are a way for users to run an executable with the permissions of the user (setuid) or group (setgid) who owns the file. For example, if you want a user to be able to perform a specific task that requires root/superuser privileges, but don't want to give them sudo or root access.
Normally, when a process on a Linux system is started it runs using the uid/gid of whatever user called it. This means it has the same privileges as the associated uid/gid would have. If neither your user, nor any of your real or effective groups have access, neither will you.
Let's walk through a simple example using the ls command. We have two subdirectories in our /topsecretfolder: secret1 and secret2. Both subdirectories are owned by root. The secret1 subdirectory allows read and execute permissions to everyone else. The secret2 subdirectory grants no privileges to everyone else.
However, when we try the same thing on topsecretfolder/secret2, we get a permission denied message. That's because when running with our "cooluser" account's privileges, the system denies ls access to the secret2 subdirectory.
Under normal circumstances, that suggests we'd need to be root or have sudo privileges to change our password. However, normal users can execute the passwd command to change their own password without sudo or root permissions.
Both executables are owned by the root user and group, and there is only one difference in the permissions. As you can see, the passwd executable has an "s" where you'd expect an "x" for the file owner's permissions. This "s" tells us the setuid bit is set.
Because the setuid bit is set, when we run the passwd command it is automatically executed as the owner of the file. Since root is the owner, the password change and required edit to /etc/shadow work.
One of the more confusing concepts when it comes to Linux file permissions is the sticky bit. In early Unix systems, the sticky bit was used to retain part of a program in swap space after a process exited. This had the effect of making programs load faster. However, that's not what the sticky bit does on modern Linux systems.
Today, the sticky bit restricts who can delete files in a directory on Linux systems. Specifically, when the sticky bit is set, only the user that owns, the user that owns the directory, or the root user can delete files within the directory. In some cases, the sticky bit is more intuitively referred to as a "restricted deletion flag" or "restricted deletion bit".
The /tmp directory is one of the most common use cases for the sticky bit. Files are frequently created in /tmp for different user accounts during normal operation of many multi-user systems. If users were able to delete one another's /tmp files, it could wreak havoc on how different applications work.
We can see that command added a "t" to the end of the directory permissions. That "t" tells us the sticky bit is set. To test that theory, let's confirm our "seconduser" account can create files in the directory but not delete files owned by "cooluser".
The simplest way to check if a file has the setuid bit set is to use ls -l . If there is an "s" in the execute field for the user, the setuid is set. For example, we can see this with the passwd executable on most *nix systems.
To set the setuid bit using octal representation we can add "4" to the front of our standard octal permissions. For example, chmod 4755 would give the owner read, write, and execute permissions, the user and group read and execute, and set the setuid bit.
With an understanding of setuid, setgid, and the sticky bit, you should now have a better understanding of Linux file permissions. Even if you don't need to create files and directories with these bits set regularly, knowing how they work is important. They impact how many different programs work. As a result understanding them can make you a better administrator and troubleshooter.
A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to digital data.[1][2] Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents. On retrieval, the calculation is repeated and, in the event the check values do not match, corrective action can be taken against data corruption. CRCs can be used for error correction (see bitfilters).[3]
CRCs are so called because the check (data verification) value is a redundancy (it expands the message without adding information) and the algorithm is based on cyclic codes. CRCs are popular because they are simple to implement in binary hardware, easy to analyze mathematically, and particularly good at detecting common errors caused by noise in transmission channels. Because the check value has a fixed length, the function that generates it is occasionally used as a hash function.
Specification of a CRC code requires definition of a so-called generator polynomial. This polynomial becomes the divisor in a polynomial long division, which takes the message as the dividend and in which the quotient is discarded and the remainder becomes the result. The important caveat is that the polynomial coefficients are calculated according to the arithmetic of a finite field, so the addition operation can always be performed bitwise-parallel (there is no carry between digits).
When a codeword is received or read, the device either compares its check value with one freshly calculated from the data block, or equivalently, performs a CRC on the whole codeword and compares the resulting check value with an expected residue constant.
The device may take corrective action, such as rereading the block or requesting that it be sent again. Otherwise, the data is assumed to be error-free (though, with some small probability, it may contain undetected errors; this is inherent in the nature of error-checking).[6]
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