ubuntu - Difference between unlink and rm on unix -


whats real different between these 2 commands? why system call delete file called unlink instead of delete?

you need understand bit original unix file system understand important question.

unlike other operating systems of era (late 60s, 70s) unix did not store file name actual directory information (of file stored on disks.) instead, unix created separate "inode table" contain directory information, , identify actual file, , allowed separate text files directories of names , inodes. originally, directory files meant manipulated other files straight text files, using same tools (cat, cut, sed, etc.) shell programmers familiar day.

one important consequence of architectural decision single file have more 1 name! each occurrence of inode in particular directory file linking inode, , known. connect file name file's inode (the "actual" file,) "linked" it, , when deleted name directory "unlinked" it.

of course, unlinking file name did not automatically mean deleting / removing file disk, because file might still known other names in other directories. inode table includes link count keep track of how many names inode (a file) known by; linking name file adds 1 link count, , unlinking removes one. when link count drops down zero, file no longer referred in directory, presumed "unwanted," , can deleted.

for reason "deletion" of file name unlinks - hence name of system call - , there important ln command create additional link file (really, file's inode,) , let known way.

other, newer operating systems , file systems have emulate / respect behavior in order comply posix standard.


Comments

Post a Comment

Popular posts from this blog

commonjs - How to write a typescript definition file for a node module that exports a function? -

consider, toml node module can use: // toml.d.ts declare module toml { export function parse(value:string):any; } declare module "toml" { export = toml; } then: /// <reference path="../../../../../defs/toml/toml.d.ts"/> import toml = require('toml'); toml.parse(...); however, node module export single function, such 'glob' ( https://github.com/isaacs/node-glob ). the node usage of module be: var glob = require("glob") glob("*.js", {}, callback(err, files) { ... }); you'd naively expect this: // glob.d.ts declare function globs(paths:string, options:any, callback:{(err:any, files:string[]):void; ...but because typescripts 'import' semantics bit strange, seems can use 'import .. = require()' statement alias modules . trying call: /// <reference path="../../../../../defs/glob/glob.d.ts"/> import blog = require('glob'); results in: error ts2072: mod...
Read more

openid - Okta: Failed to get authorization code through API call -

i'm integrating okta own idp server using okta's api. i'm implementing authorization code flow following steps below: in own server, use /api/v1/authn endpoint sessiontoken. use sessiontoken obtain authorization calling endpoint: /oauth2/v1/authorize?client_id=" + clientid + "&sessiontoken=" + sessiontoken + "&response_type=code&response_mode=query&scope=openid&redirect_uri=" + redirecturl + "&state=evanyang&nonce=" it's supposed return response status code 302 , location header containing redirect url code value. however, keep getting response status code 200 , without location header, html body saying "you using unsupported browser." , "javascript disabled on browser." according api documentation: http://developer.okta.com/docs/api/resources/oidc.html#authentication-request , sessiontoken parameter sufficient this: an okta one-time sessiontoken. allows api-based ...
Read more

ios - Change Storyboard View using Seague -

i have following code checks connection server, , depending on want change views if no connection found. nsstring *connect = [nsstring stringwithcontentsofurl:[nsurl urlwithstring:@"http://myserver.com"] encoding:nsutf8stringencoding error:nil]; if (connect == null) { [self performseguewithidentifier:@"network_failure" sender:self]; } else { // other code here } my problem not change views. have added storyboard segue between 2 views identifier of network_failure . not have navigation controller or that, problem? thanks help! no not problem. first of all, in objectivec exists nil object oriented null . must use that. so: if(connect == nil) or better: if(!connect) so due fact nil not same of null , probably code does't enter in if scope . you have been able discover breakpoint. anyway: be sure set trigger segue (line) 2 view controller , , name network_failure (that not best name. should instead view1toview2 ) as, m...
Read more