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This frequently allows commonly available software to recover the "erased" file's data. If the file data is stored on magnetic media such as a HDDeven if the file is overwritten, residual magnetic fields may allow data recovery using specialist hardware equipment. To prevent this, shred overwrites the contents of a file multiple times, using patterns chosen to maximize destruction of the residual data. Features[ edit ] shred can be invoked either on ordinary files or on devices such as hard disk partitionswhich are represented as files in Unix.
This makes sense when you realise that directories are files as well. The file is not stored "inside" a directory. Files are stored in data blocks scattered alll over the disk partition.
The directory is a special file that contains access information about all of the files references "inside" the directory. Suppose you have read access to a directory, but you do not have read access to the files in the directory.
You can still read the directory, or more corectly, the status information for that file, as returned by the stat system call. The file itself is stored elsewhere on the disk this spot is identified by the i-node number.
The "ls -i" command shows the i-node number for a file. Write permission in a directory allows you to change the contents of a directory.
Because the name of the file is stored in the directory, and not in the file, write permission in a directory allows renaming or deletion of files and does not require write permission of the file.
To be specific, if someone has write permission to your home directory, they can rename or delete your. The permissions of your. Execute permission on a directory is sometimes called search permission.
If you found a directory that gave you execute permission, but not read permission, you could use any file in that directory.
However, you must know the name. You cannot look inside the directory to find out the names of the files. Think of this type of directory as a black box. The read, write and execute permissions are stored in three different places, called user ugroup g or world or other o.
When you list this file with "ls -l" you will see -r--r--r-- 1 grymoire admin 0 Feb 1 All files have an owner and group associated with them. These permissions are determined by 9 bits in the i-node information, and are represented by the characters "rwxrwxrwx.
If the permission is not true, a dash is used to indicate lack of privilege. Some people belong to more than one group. Assume the file is in a group directory, with the group "admin", and you wanted to allow them to read and You can create a directory that has read, write and execute permission for the group.
But you want to prevent people outside of the group from reading or changing the file. The chmod command can do this.
So how can you change it to "rw-rw"? The chmod command has options, of course. You can explicitly specify u, g or o in the chmod command: They only change what is specified. If you want to change the group permission, use "g" instead of "o": The octal representative of the read, write and execute bits, "rwx" are Read 4 Write 2 Execute 1 Octal representation is pure geek talk, and was the only form that worked in the early versions of Unix.This guide shows practical examples for using the Linux unzip command, including listing the contents of a file and unzipping password-protected files However, you can use the -n switch if you want to not overwrite existing files.
Every file from the ZIP archive that has a name matching a file in the extracted folder will not overwrite. The Grymoire's C-shell (CSH) Tutorial. Check out my other tutorials on the Unix Page, and my. Check my blog Table of Contents. C shell problems.
Here's how it works: The information in each file you create gets stored on your computer's hard disk, where it's spread across multiple "data clusters," or chunks of space that each have a.
Newbie to UNIX. Need to replace a file on unix server with a new version. The file is set to read only and I cannot use the cp command because I keep getting "permission denied". The permission says that group and owner for the file is set to chwadmin and I checked and I am belong to group regardbouddhiste.coms: cp overwrite.
cp overwrites files / directories in Linux/Unix. Regular cp ususally overwrites destination files and directories: $ cp test.c bak. 70 Frequently-asked Basic UNIX Interview Questions With Answers - Download PDF file Also you can Download this "UNIX Interview Questions With Answers" as a PDF.