Last night spent a whole night answering a question about the redirect output to/dev/null in the shell. Decisive tonight also synchronous hair here, anyway no one see ~ ~ ~The following comes from a heavy Linux use patient's unsolicited answer.Answer the questions of the main question in simple language first:
What does 2>/dev/null mean in a shell program?
Answer: "2>/
The shell can often be seen: >/dev/null 2>1/dev/null represents an empty device filewhere does the > delegate redirect to, for example: echo "1111" >/home/a.txt1 means stdout standard output, the system default is 1, so ">/dev/null" is equivalent to "1>/dev/null"2 indicates stderr standard error means equivalent to, 2>
What the hell is/DEV/KVM?1./DEV/KVM device is a device file that comes out of a KVM (kernel-based virtual machine) VM2. Speaking of KVM, we have to mention that Qemu,qemu is a simulation software that runs on Linux user space. QEMU can simulate all the operating systems we can see, such as simulating Andrio,ios on the x86 platform, and, of course, simulating windows,linux (GNU), BSD. Because of the simulati
In Linux,/dev/loop is often used to create the file system image file rootfs. IMG, so that it can be downloaded to the kernel for mounting;
Http://zh.wikipedia.org/wiki//dev/loop
We have daily access to a large number of image files *. ISO, which use data files to store data on actual block devices;
First of all, you must make it clear that you need a specific file system to store files on devices such as C
What is the difference between echo and/dev/null in command for clearing file content?
We know that there are many methods to clear the file content. This article only talks about the differences between echo "And/dev/null.
1. What is the black hole device/dev/null?
In Linux, the null device is basically used to discard output streams that are no longer needed
Using/dev/zero to create a virtual hard disk/dev/zero is a special device in Linux, each time you read it, It outputs a byte (all of them are "0" in the editor). Now we can create a 10 m data file, then run the file command to view [root @ xx ~]. # Dd if =/dev/zero of = hd. img bs = 1 k count = 10000 [root @ xx ~] # File hd. img the file command hd. img is a data
Webpack-dev-server Remote Access configuration method,
The webpack-dev-server configured in the package. json file below is the Development Mode. You can use http: // localhost: 8080 or http: // 127.0.0.1: 8080 for access.
"Scripts": {"dev": "cross-env NODE_ENV = development webpack-dev-server -- open -- hot", "build
Review above:In the above section, we mainly introduce how to create a custom project in Dev. The structure of the package is briefly introduced later. Next I will complete the preparation of the package.
Chapter 2 Dev-CPP package preparation
First, let's take a look at the dev-CPP package. The Dev-CPP package has
I have introduced some examples of Python and C ++ interoperability.
Series of articles:
Python calls C/C ++ functions (1)
Python calls C ++ (2) encapsulated by boost Python)
C ++ calls Python (3)
C ++ calls Python (4)
C ++ and Python advanced application interoperability (5)
C ++ calls the pythonapi thread status and global interpretation lock (6)
It is very prone to problems, such as Unicode problems and importerror problems. So let's introduce the installation and configuration.
1. Install P
System CentOS 7
Df-h view current partition usage;
Dfisk/dev/xvda operation of the/DEV/XVDA disk (new partition and formatting)
N
P
Enter the default partition number;
Enter the default disk creation start location;
Enter the default disk creation end location;
T set the partition type
8e LVM Type
W Save
Restart
LVM into LVM Management
Lvm>pvcreate/
command:$WC-L You can also use here Document in a script, for example:
#!/bin/bash
Cat
A simple lookup program
For good (and bad) restaurants
In Cape town.
Eof
Operation Result:This was a simple lookup programfor good (and bad) Restaurantsin Cape town.The following script saves the document to the Test.txt file through the VI editor:
#!/bin/sh
FileName=test.txt
VI $filename
I
This file is created automatically from
A
Using shell commands under Linux often uses shell output redirection like this:
1>/dev/null 2>1
At the end of the shell command, we can redirect the output through the > symbol.
1. Standard input stdin file descriptor is 0, standard output stdout file descriptor is 1, standard error stderr file descriptor is 2
2./dev/null empty equipment files, equivalent to garbage cans
3. REDIRECT Symbol:>
Explain
Introduced/ dev/shm/ is a device that uses the Tmpfs file system, which is actually a special file system. the default size in Redhat is half of physical memory, so that time is not mkfs formatted. TMPFS is a memory-based virtual file system on the Linux/unix system .TMPFS can use your memory or swap partition to store the file ( that is, its storage space in virtual memory , the VM consists of real memory and swap ). Thus, TMPFS primarily stores s
/dev/zero is a special file in a Unix-like system that provides an infinite null character when the file is read. One of its main uses is to provide a character stream to initialize the data store, which is to overwrite the target data with a null character. Another common use is to produce a blank file of a specific size.You can read a null character of any size from/dev/zero. Unlike/
Setting up a fully functional ChromiumOS development environment on actual Chromebook hardware Set up environment
Export dev_dir= "/opt"
mkdir-p $DEV _dir
export chromium_dir= "$DEV _dir/chromiumos"
mkdir-p $CHROMIUM _dir
export path= "$DEV _dir/depot_tools: $PATH"
# The BOARD variable used here are specific for the Chromebook that Is
# being targeted, a more
The struct Iommu_group *group can be obtained from the device structure;
For example:
struct Iommu_group *iommu_group_get (struct device *dev)
{
struct Iommu_group *group = dev->iommu_group;
if (group)
Kobject_get (Group->devices_kobj);
return group;
}
Group = Iommu_group_get (dev);
And Iommu_group has included Iommu_domain
For example: domain = group->domain
1. Basic theory/dev/shm This file is a parasite, it's in memory.Swap is temporarily dividing an area of the hard disk into memory usage2. How to viewUse DF-LH to view/DEV/SHMUse free-m to view swap files3. Contact :/dev/shm are temporary documents4. When to useThe superiority of/DEV/SHM file is discovered by Oracle, an
the shell can often be seen: >/dev/null 2>1 The result of the command can be defined in the form of a%> output /dev/null represents an empty device file where does the > delegate redirect to, for example: echo "123" >/home/123.txt 1 means stdout standard output, the system default is 1, so ">/dev/null" is equivalent to "1>/
Q:
When grub2 boot archlinux 2011.08.19 ISO file, the error is:
Waiting 30 seconds for device/dev/Disk/by-label/xxxxError: boot device didn't show up after 30 seconds
A:
Mkdir/CDROMMount-T vfat/dev/sda1/CDROMModprobe LoopLosetup/dev/loop6/CDROM/boot/ISO/archlinux-2011.08.19-core-i686.isoLn-S/dev/loop6/
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