List page by page in linux

20 Basic ‘ls’ Command Examples in Linux

Listing files is one of the most widely undertaken tasks by ordinary Linux users and system administrators. In Linux, the ls command, short for “list” is used to list or display the contents of a directory.

This could either be your current directory or any other directory on the system. The command displays both files and subdirectories and in most cases distinguishes between different file types using color codes.

Without any command-line options, the ls command will simply list all the directory contents. However, it provides an array of handy command-line options to manipulate the output and display the desired output.

You might also like:

In this article, we’ll be discussing the basics of ls command examples with all the available various command options that it provides in Linux.

ls Command Options in Linux

The ls command takes the following syntax:

$ ls [ options ] /path/to/directory

The options section represents the command-line arguments that can be passed to manipulate the output of the command.

In this tutorial, we will cover the following ls command arguments.

Options	Description
ls -m	Lists directory contents separated by a comma.
ls -Q	Displays directory contents enclosed by quotation marks.
ls -l	Displays files in a long-list format.
ls -lh	Display file size in a human-readable format.
ls -g	Omits group ownership column.
ls -F	Adds a forward slash to directories.
ls -i	Display inode number of files and directories.
ls -a	Display all files including hidden files.
ls *.	Filters files according to the file extension.
ls -la	Displays all files and directories in long list format.
ls -R	Display files and directories recursively.
ls -r	Sort Files in reverse.
ls -X	Sort files alphabetically by file extension.
ls -tl	Display files according to file creation date and time.
ls -n	List UIDs and GIDs.

1. List Files and Directories in Linux

Running ls command without passing any command-line options or arguments, the ls command simply lists the directory contents in alphabetical order. Here we won’t be able to view details like file types, size, modified date and time, permission and links, etc.

2. Long Listing of Files in Linux

The -l command option lets you print out detailed information about the directory contents in a columnar format that includes size, modified date and time, file or directory name and owner of the file, and its permission.

Starting from the far left, we have:

• 1st column – File/directory permissions.
• 2nd column – Number of links.
• 3rd column – Name of the owner.
• 4th column – Name of the group that the file belongs to.
• 5th column – File size in bytes.
• 6th column to 8th column – Last modification date.
• 9th column – File / Directory name.

3. List Hidden Files and Directories

Hidden files are special files that store user settings and configuration files, which are used by running programs and services for reading and storing information.

For example. the .bashrc file is a script that contains user settings and configurations of the currently logged-in user, which include command aliases, shell history, the coloring of the terminal font, etc.

The .bash_logout file is executed when you log out of your bash sessions. It’s mainly used for cleanup purposes i.e. carrying out any operations that need to be performed once you exit the bash shell.

To list hidden files, pass the -a option as shown, which displays both hidden files and directories.

4. List All Files in Linux

As you have noticed the -a option not only lists hidden files but all the files and directories. For better viewing, you can use the -la option

5. Display File Size in a Human-readable Format

To present the output in a better format, add the -h flag to print the file size in a human-readable format. From the output, the file size is displayed in Kilobytes, Megabytes, and Gigabytes. By all means, this looks more presentable.

6. Distinguish Directories and Files in Linux

When running the ls command, it’s not always easy to make a clear distinction between files and directories. The -F option adds a forward slash (/) to directories, making it easier for them to stand out from the rest of the files.

7. Sorting Files in Reverse Order

By default, the ls command sorts files and directories alphabetically (From A – Z). You can opt to sort the directory contents in reverse order using the -r option.

In addition, you can sort the file extensions alphabetically using the -X flag.

8. List Files Recursively in Linux

The -R flag lists files recursively. First, the command lists all the files and directories in your current directory, then proceeds to display files contained in individual directories and subdirectories.

In the following example, the files in individual directories have been listed as well.

9. Sort Files By Modification Time in Linux

The ls -ltr command shows the files in the long listing format in reverse sorted by modification time, which means it will display detailed information about each file or directory in reverse order based on their last modified date/time stamp.

10. Sort Files By Newest to Oldest in Linux

You can sort files by time and date using the -t option, which sorts the files in order starting from the newest to the oldest.

11. Sort Files by File Size in Linux

With a combination of -lS option, it will displays file size in descending order (biggest to smallest in size).

12. List File Inode Number in Linux

You can display the files and directories’ inode numbers using the -i option as shown.

13. List Files and Directories Separated by Commas

The -m flag lists the directory contents one after the other separated by a comma.

With the -Q flag, all the directory contents are enclosed by double quotation marks as shown.

14. Omit Group Ownership in a Long-List Format

When used with the -l command option, the ls command prints both user and group ownership of the file. You can opt to omit the group column by passing the -g option.

15. List Specific File Types or Extensions

To list specific file types or extensions, use the wildcard notation (*) followed by the file extension.

For example, to display all files with a .jpg extension, run the command:

Similarly, to list all PDF files, run the command:

16. List the UID and GID of Files

To display the UID and GID of files and directories, use the -n option as shown.

17. Check ls Command Version

If you are a little curious and want to check the version of the ls command, you can do so as follows:

From the output, you can see that we are running ls version 9.1.

18. Show ls Command Help Page

The ls program provides a wealth of command-line options. What we have covered are just some of the commonly used ones. For a comprehensive list of all the command options, run the following command:

Optionally, you can visit the man pages by running:

19. List Directory Information in Linux

With the ls -l command list files under directory /tmp. Wherein with -ld options, it will display information of the /tmp directory.

20. Create ls Command Aliase

We have made an alias for the ls command when we execute the ls command it will take the -l option by default and display a long listing as mentioned earlier.

To view a number of aliases available in your system, use the below alias command and the same can be unalias as shown below example.

To remove an alias previously defined, just use the unalias command.

In this guide, we have demonstrated how to use the ls command to view the contents of a folder or directory. In addition, we went a step further and explored command options that can be used with the ls command in Linux.

In our next article, we’ll cover more advanced ls commands with their examples. Also, I suggest you go through some interview questions on the ls command, and also if we’ve missed anything in the list, please update us via the comment section.

Источник

Walking page tables of a process in Linux

i’m trying to navigate the page tables for a process in linux. In a kernel module i realized the following function:

static struct page *walk_page_table(unsigned long addr) < pgd_t *pgd; pte_t *ptep, pte; pud_t *pud; pmd_t *pmd; struct page *page = NULL; struct mm_struct *mm = current->mm; pgd = pgd_offset(mm, addr); if (pgd_none(*pgd) || pgd_bad(*pgd)) goto out; printk(KERN_NOTICE "Valid pgd"); pud = pud_offset(pgd, addr); if (pud_none(*pud) || pud_bad(*pud)) goto out; printk(KERN_NOTICE "Valid pud"); pmd = pmd_offset(pud, addr); if (pmd_none(*pmd) || pmd_bad(*pmd)) goto out; printk(KERN_NOTICE "Valid pmd"); ptep = pte_offset_map(pmd, addr); if (!ptep) goto out; pte = *ptep; page = pte_page(pte); if (page) printk(KERN_INFO "page frame struct is @ %p", page); out: return page; > 

static int my_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long addr)

The strange thing is that calling ioctl in a user space process, this segfaults. but it seems that the way i’m looking for the page table entry is correct because with dmesg i obtain for example for each ioctl call:

[ 1721.437104] Valid pgd [ 1721.437108] Valid pud [ 1721.437108] Valid pmd [ 1721.437110] page frame struct is @ c17d9b80 

So why the process can’t complete correcly the `ioctl’ call? Maybe i have to lock something before navigating the page tables? I’m working with kernel 2.6.35-22 and three levels page tables. Thank you all!

Источник

How to get list of all pages that belong to a process (linux)

Is there a way to get a list of all pages owned by a process in Linux kernel? I would need to call ‘page_free()’on those pages. Please let me know!!

Are you asking for a Linux kernel command, or something more in relation to Android/C? I know that Linux has a ps command that shows processes, and if you add an ‘x’ after it ( ps x ), it will show you a more extensive list. Here is some documentation: unixhelp.ed.ac.uk/CGI/man-cgi?ps

I am asking if there is a «linux kernel API» that gives a list of pages associated with a process or if there is a way to get this list by having a process id.

You can try ps pid , where pid is your process id. This will give you all pages linked to the given process id.

looks like you have mistaken my question. I was asking if there is a way inside the kernel code to call some ‘kernel api’ that gives a list of all pages associated with a process. This is something to do with the task_struct of that process.

1 Answer 1

If you want get a list of all the physical pages to collect state, you can write a small kernel module to achieve this, declare a struct page *p for (for physical page on the system), there is a exported symbol ./mm/memory.c:mem_map pointing to the page with PFN = 0. You can use get_num_physpage() to get total number of physical pages. Then you should be able to walk to the array to get physical page stats.

If its all pages of a process: it looks like you have to walk the page tables of a process

Linked

Related

Hot Network Questions

Subscribe to RSS

To subscribe to this RSS feed, copy and paste this URL into your RSS reader.

Site design / logo © 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA . rev 2023.7.14.43533

By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy.

Источник