How can I symlink a file in Linux? [closed] - linux

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I want to make a symbolic link in Linux. I have written this Bash command where the first path is the folder I want link into and the second path is the compiled source.
ln -s '+basebuild+'/IpDome-kernel/kernel /home/build/sandbox/gen2/basebuild/IpDome-kernel/kernal
Is this correct?

To create a new symlink (will fail if symlink exists already):
ln -s /path/to/file /path/to/symlink
To create or update a symlink:
ln -sf /path/to/file /path/to/symlink

ln -s TARGET LINK_NAME
Where the -s makes it symbolic.

ln -s EXISTING_FILE_OR_DIRECTORY SYMLINK_NAME

ln -s target linkName
You can have a look at the man page here:
http://linux.die.net/man/1/ln

(Because an ASCII picture is worth a thousand characters.)
An arrow may be a helpful mnemonic, especially since that's almost exactly how it looks in Emacs' dired.
And big picture so you don't get it confused with the Windows' version
Linux:
ln -s target <- linkName
Windows:
mklink linkName -> target
You could also look at these as
ln -s "to-here" <- "from-here"
mklink "from-here" -> "to-here"
The from-here should not exist yet, it is to be created, while the to-here should already exist (IIRC).
(I always get mixed up on whether various commands and arguments should involve a pre-existing location, or one to be made.)
EDIT: It's still sinking in slowly for me; I have another way I've written in my notes.
ln -s (target exists) (link is made)
mklink (link is made) (target exists)

ln -s source_file target_file
http://unixhelp.ed.ac.uk/CGI/man-cgi?ln

To the original question:
'ln -s '+basebuild+'/IpDome-kernel/kernel /home/build/sandbox/gen2/basebuild/IpDome-kernel/kernal'
This will indeed create a symbolic link (-s) from the file/directory:
<basebuild>/IpDome-kernel/kernel
to your new link
/home/build/sandbox/gen2/basebuild/IpDome-kernel/kernal
Here's a few ways to help you remember:
First, there's the man page for ln. You can access this via searching "man ln" in google, or just open a terminal window and type man ln and you'll get the same information. The man page clearly states:
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)
If having to search or read through a man page every time isn't for you, maybe you'll have an easier time remembering that all nix commands work the same way:
cp /file/that/exists /location/for/new/file
mv /file/that/exists /location/its/moving/to
ln /file/that/exists /the/new/link
cp copies a file that currently exists (the first argument) to a new file (the second argument).
mv moves a file that currently exists (the first argument) to a new place (the second argument)
Likewise ln links a file that currently exists (the first argument) to a new link (the second argument)*
The final option I would like to suggest is you can create your own man pages that are easy to read and easy (for you) to find/remember. Just make a simple shell script that gives you the hint you need. For example♦:
In your .bash_aliases file you can place something like:
commandsfx() {
echo "Symlink: ln -s /path/to/file /path/to/symlink"
echo "Copy: cp /file/to/copy /destination/to/send/copy"
}
alias 'cmds'=commandsfx
Then when you need it, from the command line just type cmds and you'll get back the proper syntax in a way you can quickly read and understand it. You can make these functions as advanced as you'd like to get what what information you need, it's up to you. You could even make them interactive so you just have to follow the prompts.. something like:
makesymlink() {
echo "Symlink name:"
read sym
echo "File to link to:"
read fil
ln -s $fil $sym
}
alias 'symlink'=makesymlink
* - well obviously they can all take different parameters and do different things and can work on files as well as directories... but the premise is the same
♦ - examples using the bash shell

ln [-Ffhinsv] source_file [target_file]
link, ln -- make links
-s Create a symbolic link.
A symbolic link contains the name of the file to which it is linked.
An ln command appeared in Version 1 AT&T UNIX.

Creating Symbolic links or Soft-links on Linux:
Open Bash prompt and type the below mentioned command to make a symbolic link to your file:
A) Goto the folder where you want to create a soft link and typeout the command as mentioned below:
$ ln -s (path-to-file) (symbolic-link-to-file)
$ ln -s /home/user/file new-file
B) Goto your new-file name path and type:
$ ls -lrt (To see if the new-file is linked to the file or not)
Example:
user#user-DT:[~/Desktop/soft]# ln -s /home/user/Desktop/soft/File_B /home/user/Desktop/soft/File_C
user#user-DT:[~/Desktop/soft]# ls -lrt
total 0
-rw-rw-r-- 1 user user 0 Dec 27 16:51 File_B
-rw-rw-r-- 1 user user 0 Dec 27 16:51 File_A
lrwxrwxrwx 1 user user 31 Dec 27 16:53 File_C -> /home/user/Desktop/soft/File_B
Note: Where, File_C -> /home/user/Desktop/soft/File_B Means, File_C is symbolically linked to File_B

ln -s sourcepath linkpathname
Note:
-s makes symbolic links instead of hard links

This is Stack Overflow so I assume you want code:
All following code assumes that you want to create a symbolic link named /tmp/link that links to /tmp/realfile.
CAUTION: Although this code checks for errors, it does NOT check if /tmp/realfile actually exists ! This is because a dead link is still valid and depending on your code you might (rarely) want to create the link before the real file.
Shell (bash, zsh, ...)
#!/bin/sh
ln -s /tmp/realfile /tmp/link
Real simple, just like you would do it on the command line (which is the shell). All error handling is done by the shell interpreter. This code assumes that you have a working shell interpreter at /bin/sh .
If needed you could still implement your own error handling by using the $? variable which will only be set to 0 if the link was successfully created.
C and C++
#include <unistd.h>
#include <stdio.h>
int main () {
if( symlink("/tmp/realfile", "/tmp/link") != 0 )
perror("Can't create the symlink");
}
symlink only returns 0 when the link can be created. In other cases I'm using perror to tell more about the problem.
Perl
#!/usr/bin/perl
if( symlink("/tmp/realfile", "/tmp/link") != 1) {
print STDERR "Can't create the symlink: $!\n"
}
This code assumes you have a perl 5 interpreter at /usr/bin/perl. symlink only returns 1 if the link can be created. In other cases I'm printing the failure reason to the standard error output.

If you are in the directory where you want to create symlink, then ignore second path.
cd myfolder
ln -s target
It will create symlink of target inside myfolder.
General syntax
ln -s TARGET LINK_NAME

I'd like to present a plainer-English version of the descriptions already presented.
ln -s /path-text/of-symbolic-link /path/to/file-to-hold-that-text
The "ln" command creates a link-FILE, and the "-s" specifies that the type of link will be symbolic. An example of a symbolic-link file can be found in a WINE installation (using "ls -la" to show one line of the directory contents):
lrwxrwxrwx 1 me power 11 Jan 1 00:01 a: -> /mnt/floppy
Standard file-info stuff is at left (although note the first character is an "l" for "link"); the file-name is "a:" and the "->" also indicates the file is a link. It basically tells WINE how Windows "Drive A:" is to be associated with a floppy drive in Linux. To actually create a symbolic link SIMILAR to that (in current directory, and to actually do this for WINE is more complicated; use the "winecfg" utility):
ln -s /mnt/floppy a: //will not work if file a: already exists

To create a symbolic link /soft link, use:
ln -s {source-filename} {symbolic-filename}
e.g.:
ln -s file1 link1

Links are basically of two types:
Symbolic links (soft): link to a symbolic path indicating the abstract location of another file
Hard links: link to the specific location of physical data.
Example 1:
ln /root/file1 /root/file2
The above is an example of a hard link where you can have a copy of your physical data.
Example 2:
ln -s /path/to/file1.txt /path/to/file2.txt
The above command will create a symbolic link to file1.txt.
If you delete a source file then you won't have anything to the destination in soft.
When you do:
ls -lai
You'll see that there is a different inode number for the symlinks.
For more details, you can read the man page of ln on your Linux OS.

There are two types of links:
symbolic links: Refer to a symbolic path indicating the abstract location of another file
hard links: Refer to the specific location of physical data.
In your case symlinks:
ln -s source target
you can refer to http://man7.org/linux/man-pages/man7/symlink.7.html
you can create too hard links
A hard link to a file is indistinguishable from the original directory entry; any changes to a file are effectively independent of the name used to reference the file. Hard links may not normally refer to directories and may not span file systems.
ln source link

I find a bit confusing the terminologies "target" and "directory" in the man information.
The target is the folder that we are symlinking to and the directory the actual symlink (not the directory that you will be symlinking to), if anyone is experiencing the same confusion, don't feel alone.
This is my interpretation of creating a Symlink (in linux):
ln -s /FULL/PATH/FOLDER-OR-FILE-SYMLINKING-TO NAME-OF-YOUR-SYMLINK
You can navigate to the folder where you want to create the symlink and run the command or specify the FULL PATH for your symlink instead of NAME-OF-YOUR-SYMLINK.
cd /FULL/PATH/TO/MY-SYMLINK-PARENT-FOLDER
ln -s /FULL/PATH/FOLDER-OR-FILE-SYMLINKING-TO NAME-OF-YOUR-SYMLINK
OR
ln -s /FULL/PATH/FOLDER-OR-FILE-SYMLINKING-TO /FULL/PATH/TO/MY-SYMLINK-PARENT-FOLDER/NAME-OF-YOUR-SYMLINK
I hope this helps to those (still) slighly confused.

How to create symlink in vagrant.
Steps:
In vagrant file create a synced folder. e.g config.vm.synced_folder "F:/Sunburst/source/sunburst/lms", "/source"
F:/Sunburst/source/sunburst/lms :- where the source code, /source :- directory path inside the vagrant
Vagrant up and type vagrant ssh and go to source directory e.g cd source
Verify your source code folder structure is available in the source directory. e.g /source/local
Then go to the guest machine directory where the files which are associate with the browser. After get backup of the file. e.g sudo mv local local_bk
Then create symlink e.g sudo ln -s /source/local local. local mean link-name (folder name in guest machine which you are going to link)
if you need to remove the symlink :- Type sudo rm local

Related

How to show '->' in front of the directory information in Linux when do ll -a?

Actually as shown bellow I wondered
How to show '->' in front of the directory information in Linux when do ll -a?
Is it something related to repository/git or it is done by another person intentionally?
The printed line with the -> is a symbolic link. Not really a directory (or a standard file).
The name of the link is latest (size of 5 characters). The target of this link is 9.0.2 (in the same directory).
So it's done intentionally by another person or a install program.
Read man ln for futher information. ln is the command for create links.
There is no relation with Git or whatelse like it.

softlink to binary always use home folder path (instead of current folder)

kdevelop provides this AppImage binary:
wget -O KDevelop.AppImage https://download.kde.org/stable/kdevelop/5.1.1/bin/linux/KDevelop-5.1.1-x86_64.AppImage
chmod +x KDevelop.AppImage
./KDevelop.AppImage
It works well. So I want to make a soft link called kd to that binary in /usr/bin, eg:
/usr/bin/sudo ln -s KDevelop-5.1.1-x86_64.AppImage kd
Now if I run kd file1, I'd expect that it would open a file name file1 in the current folder, but it always tries to open a file name file1 in my home folder - which is not where it should be.
Is there some way to fix this issue?
Some possible causes:
The application always assumes that you want to open files in your home directory, effectively or literally prepending $HOME to the path. This would be a bug in any *nix program, and should be reported.
The application behaves differently when $(basename "$0") is not KDevelop.AppImage (what #Scheff said).
You are actually running a different kd.
Possible workarounds/investigations:
Pass the full path to the file on the command line. If it tries to open /home/you//full/path/you/provided it is obviously buggy, and you have a test case. If it does not, then there might be some gotcha to what your $PWD actually is. Try checking its value before running.
Symlink with the same name, using sudo ln -s KDevelop-5.1.1-x86_64.AppImage /usr/bin, and try running that. If it behaves the same, you've at least proven that the symlink is not the problem.
Run type -a kd and verify that your /usr/bin/kd comes up first. If not there might be an alias or shell built-in which takes precedence.
That said, what is the actual error message?

Is it possible to edit a symlink with a text editor?

When we create a symlink, the number of bytes the symlink takes up is exactly the length of the origin it points to. For instance,
$ ln -s dest link1
$ ln -s longer_dest link2
$ ls -l
lrwxrwxrwx 1 username 4 Mar 26 20:21 link1 -> dest
lrwxrwxrwx 1 username 11 Mar 26 20:21 link2 -> longer_dest
where link1 takes up 4 bytes, which is the length of dest; link2 takes up 11 bytes, which is the length of longer_dest. Therefore, symlinks are in fact no more than the destination path stored in plain text. So I am wondering if it is possible to edit (the destination) of a symlink in text editors, preferably Emacs. I googled for a while and couldn't find anyone talking about this. Note that this question is purely out of curiosity; I know full well that I can overwrite a symlink by ln -f -s.
Yes, in Emacs this is possible in dired-mode, specifically wdired (writable dired) mode.
Note, dired and wdired both are built-in packages.
Here's an example...
(BTW: I'm using Smex to give Emacs M-x command search & execute a more ergonomic UI + fuzzy matching)
It's possible in principle, but the editor would need to specifically support it, since reading the destination of a symlink requires a special system call: readlink().
You're unlikely to find any editors that actually do this, since it's not very useful, and conflicts with what most users want the editor to do when asked to open a symlink: open the file that it points to.
As per the Storage of symbolic links section in Wikipedia's article Symbolic Links, the symlinks are stored in an inode. This inode is a data structure containing several information about the file in question - as per this thread, the touch command can be used to change some of its values. So, it may not be possible to modify it by using a text editor, due to the problems that #Wyzard mentioned, but it might be modifiable by using some other command-line tools like touch.
I hope this helps!
It's not possible directly, as others have already pointed out, but of course you can write a script for it. Here's one I came up with when I had to change lots of symlinks
#! /bin/bash
tmp=$(mktemp)
trap "rm $tmp" EXIT
while [ ! -z "$1" ]; do
filename="$1"; shift
if [ ! -h "$filename" ]; then
echo "Not a symlink: $filename";
continue
fi
stat -c "%N" "$filename" >> $tmp
done
emacs $tmp
while read filename linkname; do
ln -sf "$linkname" "$filename"
done < <(sed "s/'\(.*\)' -> '\(.*\)'/\1 \2/" $tmp)
It worked for me, but it's certainly not perfect, so use at your own risk...

linux: what is the difference between these two symbolic link commands

I am trying to create a symbolic link on the server with the command ln -s,
Option 1:
ln -s /home/thejobco/public_html/JCCore/ajax_search /home/thejobco/public_html/demo/typo3conf/ext/
result 1:
ajax_search -> /home/thejobco/public_html/JCCore/ajax_search
Option 2:
ln -s /home/thejobco/public_html/JCCore/ajax_search/ /home/thejobco/public_html/demo/typo3conf/ext/
result 2:
ajax_search -> /home/thejobco/public_html/JCCore/ajax_search/
Question:
I want to know if the above two options are the same, or there is different between them? Option 1 does not have /, option 2 has /, but both of them work well, so just wonder which is the standard way?
A symbolic link is implemented as a file containing the name of the target.
There is a minor difference, as you've seen: one of the symlinks has a trailing /, and the other doesn't. You can see the difference in the output of ls -l; on a lower level, this shows up as a difference in the path returned by the readlink() system call.
But there should be no functional difference between them -- as long as the target is a directory. Either can be used to access the linked directory.
For a target that's not a directory, this:
ln -s /etc/motd good_link
ln -s /etc/motd/ bad_link
will result in good_link being a valid way to access /etc/motd, and bad_link resulting in a not a directory error.

How do I create a multi-level softlink in Linux or can this be done? [closed]

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I have inherited old scripts which cannot be touched - don't ask. It references software installed at location /SuperSoft/SomeSoft/
The new version of the software, remade since the buyout, installs at location
/usr/local/SomeSoft
I've been having a bear trying to create the following softlink at the root level:
ln -s SuperSoft/SomeSoft/ /usr/local/SomeSoft/
I would hate to create a SuperSoft directory at the root level. Can this be done?
Having the same files in two parts of the filesystem can also be accomplished with mount.
From "man mount" on linux:
Since Linux 2.4.0 it is possible to remount part of the file
hierarchy somewhere else. The call is
mount --bind olddir newdir
or shortoption
mount -B olddir newdir
or fstab entry is:
/olddir /newdir none bind
After this call the same contents is accessible in two places.
Was hard to get want you want. Use this link:
ln -s /usr/local/SuperSoft/ /SuperSoft/
Now you can use the following ls to browse the contents of /SuperSoft/SomeSoft:
ls -al /SuperSoft/SomeSoft
You're looking for the first form of ln:
SYNOPSIS
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)
Using -s as an option, since you want a symbolic link. The TARGET is the "value" of the symlink--i.e., what the link is going to be pointing to. The LINK_NAME is the actual location of the link being created. So, to create a symlink at /SuperSoft/SomeSoft that points to /usr/local/SomeSoft, you would do:
ln -s /usr/local/SomeSoft /SuperSoft/SomeSoft
Which would look like this in a long listing:
$ ls -l /SuperSoft/SomeSoft
lrwxrwxrwx 1 user group 18 May 23 13:43 /SuperSoft/SomeSoft -> /usr/local/SomeSoft
So you can install the new version of your software as normal to /usr/local, and your existing scripts which cannot be modified will be pointed to /usr/local when they try to access /SuperSoft/SomeSoft.
Note that doing it this way assumes there exists a directory called /SuperSoft. If this isn't an option for you (or if you just don't want to do it), then you can create a symlink at /SuperSoft that points to /usr/local (ln -s /usr/local /SuperSoft), since accessing /Supersoft/SomeSoft will turn into /usr/local/SomeSoft. I'd recommend against this though, as it's not very clean.
UPDATE:
Another way to make it so that /SuperSoft is a symlink is to do:
mkdir /usr/local/SuperSoft
ln -s /usr/local/SuperSoft /SuperSoft
ln -s /usr/local/SomeSoft /SuperSoft/SomeSoft
In any case, there needs to be a directory that houses the link pointing to /user/local/SomeSoft.
No, you cannot create a symlink that is a directory path. A symlink is just an entry in an ordinary directory, so it must conform to all regular naming rules.
If you want a symlink "/SuperSoft/SomeSoft", then "/SuperSoft" must exist. It could be a directory, or it could be a symlink to elsewhere, but it has to be something.
If you absolutely want to avoid creating a new directory in /, then you could create a fake / with the appropriate directories/symlinks/etc and run the scripts chrooted() there. But that's a bunch more setup than just making one directory.

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