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SYMLINK(7)                 Linux Programmer's ManualSYMLINK(7)NAME       symlink - symbolic link handlingDESCRIPTION       Symbolic  links  are files that act as pointers to other files.  To un-       derstand their behavior, you must first understand how hard links work.       A hard link to a file is indistinguishable from the original  file  be-       cause it is a reference to the object underlying the original filename.       (To be precise: each of the hard links to a file is a reference to  the       same inode number, where an inode number is an index into the inode ta-       ble, which contains metadata about all  files  on  a  filesystem.   Seestat(2).)  Changes to a file are independent of the name used to refer-       ence the file.  Hard links may not refer to directories (to prevent the       possibility  of  loops  within the filesystem tree, which would confuse       many programs) and may not refer to files on different filesystems (be-       cause inode numbers are not unique across filesystems).       A  symbolic  link is a special type of file whose contents are a string       that is the pathname of another  file,  the  file  to  which  the  link       refers.   (The  contents  of  a  symbolic  link can be read using read-link(2).)  In other words, a symbolic link  is  a  pointer  to  another       name, and not to an underlying object.  For this reason, symbolic links       may refer to directories and may cross filesystem boundaries.       There is no requirement that the pathname referred  to  by  a  symbolic       link should exist.  A symbolic link that refers to a pathname that does       not exist is said to be a dangling link.       Because a symbolic link  and  its  referenced  object  coexist  in  the       filesystem  name  space,  confusion can arise in distinguishing between       the link itself and the referenced object.  On historical systems, com-       mands  and system calls adopted their own link-following conventions in       a somewhat ad-hoc fashion.  Rules for a more uniform approach, as  they       are  implemented  on Linux and other systems, are outlined here.  It is       important that site-local applications also conform to these rules,  so       that the user interface can be as consistent as possible.   Symbolic link ownership, permissions, and timestamps       The  owner  and group of an existing symbolic link can be changed usinglchown(2).  The only time that the ownership of a symbolic link matters       is  when  the  link is being removed or renamed in a directory that has       the sticky bit set (seestat(2)).       The last access and last modification timestamps of a symbolic link can       be changed usingutimensat(2) orlutimes(3).       On Linux, the permissions of a symbolic link are not used in any opera-       tions; the permissions are always 0777 (read, write,  and  execute  for       all  user categories), and can't be changed.  (Note that there are some       "magic" symbolic links in the /proc directory  tree--for  example,  the       /proc/[pid]/fd/* files--that have different permissions.)   Obtaining a file descriptor that refers to a symbolic link       Using  the  combination  of  the O_PATH and O_NOFOLLOW flags toopen(2)       yields a file descriptor that can be passed as the  dirfd  argument  in       system  calls  such asfstatat(2),fchownat(2),fchmodat(2),linkat(2),       andreadlinkat(2), in order to operate  on  the  symbolic  link  itself       (rather than the file to which it refers).       By  default  (i.e., if the AT_SYMLINK_FOLLOW flag is not specified), ifname_to_handle_at(2) is applied to a symbolic link, it yields a  handle       for  the  symbolic link (rather than the file to which it refers).  One       can then obtain a file descriptor for the symbolic  link  (rather  than       the  file to which it refers) by specifying the O_PATH flag in a subse-       quent call toopen_by_handle_at(2).  Again, that file descriptor can be       used in the aforementioned system calls to operate on the symbolic link       itself.   Handling of symbolic links by system calls and commands       Symbolic links are handled either by operating on the link  itself,  or       by  operating  on  the  object  referred to by the link.  In the latter       case, an application or system call is said to follow the  link.   Sym-       bolic  links may refer to other symbolic links, in which case the links       are dereferenced until an object that is not a symbolic link is  found,       a symbolic link that refers to a file which does not exist is found, or       a loop is detected.  (Loop detection is done by placing an upper  limit       on  the  number  of links that may be followed, and an error results if       this limit is exceeded.)       There are three separate areas that need to be discussed.  They are  as       follows:       1. Symbolic links used as filename arguments for system calls.       2. Symbolic links specified as command-line arguments to utilities that          are not traversing a file tree.       3. Symbolic links encountered by utilities that are traversing  a  file          tree (either specified on the command line or encountered as part of          the file hierarchy walk).   System calls       The first area is symbolic links used as filename arguments for  system       calls.       Except as noted below, all system calls follow symbolic links.  For ex-       ample, if there were a symbolic link slink  which  pointed  to  a  file       named  afile, the system call open("slink" ...) would return a file de-       scriptor referring to the file afile.       Various system calls do not follow links, and operate on  the  symbolic       link  itself.   They  are:lchown(2),lgetxattr(2),llistxattr(2), lre-movexattr(2),lsetxattr(2),lstat(2),readlink(2),rename(2),rmdir(2),       andunlink(2).       Certain other system calls optionally follow symbolic links.  They are:faccessat(2),fchownat(2),fstatat(2),linkat(2),name_to_handle_at(2),open(2),openat(2),open_by_handle_at(2), andutimensat(2); see their       manual pages for details.  Becauseremove(3) is an alias forunlink(2),       that  library  function  also  does  not  follow  symbolic links.  Whenrmdir(2) is applied to a symbolic link, it fails with the  error  ENOT-       DIR.link(2)  warrants  special  discussion.   POSIX.1-2001  specifies  thatlink(2) should dereference oldpath if it is a symbolic link.   However,       Linux  does  not  do  this.   (By default, Solaris is the same, but the       POSIX.1-2001 specified behavior can be obtained with suitable  compiler       options.)   POSIX.1-2008  changed the specification to allow either be-       havior in an implementation.   Commands not traversing a file tree       The second area is symbolic links, specified as  command-line  filename       arguments, to commands which are not traversing a file tree.       Except as noted below, commands follow symbolic links named as command-       line arguments.  For example, if there were a symbolic link slink which       pointed  to a file named afile, the command cat slink would display the       contents of the file afile.       It is important to realize that this rule includes commands  which  may       optionally  traverse file trees; for example, the command chown file is       included in this rule, while the command chown -R file, which  performs       a  tree traversal, is not.  (The latter is described in the third area,       below.)       If it is explicitly intended that the command operate on  the  symbolic       link instead of following the symbolic link--for example, it is desired       that chown slink change the  ownership  of  the  file  that  slink  is,       whether it is a symbolic link or not--the -h option should be used.  In       the above example, chown root slink would change the ownership  of  the       file  referred  to by slink, while chown -h root slink would change the       ownership of slink itself.       There are some exceptions to this rule:       * Themv(1) andrm(1) commands do not follow symbolic  links  named  as         arguments,  but  respectively  attempt  to  rename  and  delete them.         (Note, if the symbolic link references a file via  a  relative  path,         moving  it  to another directory may very well cause it to stop work-         ing, since the path may no longer be correct.)       * Thels(1) command is also an exception to this rule.  For compatibil-         ity  with historic systems (whenls(1) is not doing a tree walk--that         is, -R option is not specified), thels(1) command  follows  symbolic         links  named  as arguments if the -H or -L option is specified, or if         the -F, -d, or -l options are not specified.  (Thels(1)  command  is         the only command where the -H and -L options affect its behavior even         though it is not doing a walk of a file tree.)       * Thefile(1) command is also an exception to this rule.   Thefile(1)         command  does not follow symbolic links named as argument by default.         Thefile(1) command does follow symbolic links named as  argument  if         the -L option is specified.   Commands traversing a file tree       The following commands either optionally or always traverse file trees:chgrp(1),chmod(1),chown(1),cp(1),du(1),find(1),ls(1),pax(1),rm(1), andtar(1).       It  is  important  to realize that the following rules apply equally to       symbolic links encountered during the file tree traversal and  symbolic       links listed as command-line arguments.       The  first  rule  applies  to symbolic links that reference files other       than directories.  Operations that apply to  symbolic  links  are  per-       formed on the links themselves, but otherwise the links are ignored.       The  command  rm -r  slink  directory will remove slink, as well as any       symbolic links encountered in the tree traversal of directory,  because       symbolic  links  may be removed.  In no case willrm(1) affect the file       referred to by slink.       The second rule applies to symbolic links that  refer  to  directories.       Symbolic links that refer to directories are never followed by default.       This is often referred to as a "physical" walk, as opposed to a  "logi-       cal"  walk  (where  symbolic  links  that refer to directories are fol-       lowed).       Certain conventions are (should be) followed as consistently as  possi-       ble by commands that perform file tree walks:       * A  command can be made to follow any symbolic links named on the com-         mand line, regardless of the type of file they reference, by specify-         ing  the -H (for "half-logical") flag.  This flag is intended to make         the command-line name space look like the logical name space.  (Note,         for  commands that do not always do file tree traversals, the -H flag         will be ignored if the -R flag is not also specified.)         For example, the command chown -HR user slink will traverse the  file         hierarchy  rooted  in  the file pointed to by slink.  Note, the -H is         not the same as the previously discussed -h flag.  The -H flag causes         symbolic  links  specified on the command line to be dereferenced for         the purposes of both the action to be performed and  the  tree  walk,         and  it is as if the user had specified the name of the file to which         the symbolic link pointed.       * A command can be made to follow any symbolic links named on the  com-         mand  line, as well as any symbolic links encountered during the tra-         versal, regardless of the type of file they reference, by  specifying         the  -L  (for "logical") flag.  This flag is intended to make the en-         tire name space look like the logical name space.   (Note,  for  com-         mands that do not always do file tree traversals, the -L flag will be         ignored if the -R flag is not also specified.)         For example, the command chown -LR user slink will change  the  owner         of  the  file  referred to by slink.  If slink refers to a directory,         chown will traverse the file hierarchy rooted in the  directory  that         it references.  In addition, if any symbolic links are encountered in         any file tree that chown traverses, they will be treated in the  same         fashion as slink.       * A  command  can be made to provide the default behavior by specifying         the -P (for "physical") flag.  This flag is intended to make the  en-         tire name space look like the physical name space.       For  commands  that  do not by default do file tree traversals, the -H,       -L, and -P flags are ignored if the -R flag is not also specified.   In       addition,  you  may  specify the -H, -L, and -P options more than once;       the last one specified determines the command's behavior.  This is  in-       tended  to permit you to alias commands to behave one way or the other,       and then override that behavior on the command line.       Thels(1) andrm(1) commands have exceptions to these rules:       * Therm(1) command operates on the symbolic link, and not the file  it         references,  and  therefore never follows a symbolic link.  Therm(1)         command does not support the -H, -L, or -P options.       * To maintain compatibility with historic systems,  thels(1)  command         acts  a  little  differently.  If you do not specify the -F, -d or -l         options,ls(1) will follow symbolic links specified  on  the  command         line.  If the -L flag is specified,ls(1) follows all symbolic links,         regardless of their type, whether specified on the  command  line  or         encountered in the tree walk.SEE ALSOchgrp(1),chmod(1),find(1),ln(1),ls(1),mv(1),namei(1),rm(1),lchown(2),link(2),lstat(2),readlink(2),rename(2),symlink(2),  un-link(2),utimensat(2),lutimes(3),path_resolution(7)COLOPHON       This  page  is  part of release 5.05 of the Linux man-pages project.  A       description of the project, information about reporting bugs,  and  the       latest     version     of     this    page,    can    be    found    at       https://www.kernel.org/doc/man-pages/.Linux                             2016-10-08SYMLINK(7)