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nu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 use toggle use subsection 1 1 options 1 2 octal notation 1 3 symbolic notation 2 examples 3 see also 4 notes 5 references 6 external links toggle the table of contents chmod 33 languages العربية asturianu azərbaycanca català کوردی čeština deutsch español euskara فارسی suomi français עברית हिन्दी hrvatski magyar italiano 日本語 한국어 lombard latviešu norsk bokmål polski português română русский slovenščina svenska தமிழ் türkçe українська tiếng việt 中文 edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikibooks wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia shell command for changing access permissions of a file chmod original author at t bell laboratories developers various open source and commercial developers release 3 november 1971 54 years ago 1971 11 03 written in plan 9 c operating system unix unix like plan 9 inferno ibm i platform cross platform type command license coreutils gplv3 plan 9 mit license chmod is a shell command for changing access permissions and special mode flags of files including special files such as directories the name is short for ch ange mod e where mode refers to the permissions and flags collectively 1 2 the command originated in at t unix version 1 and was exclusive to unix and unix like operating systems until it was ported to other operating systems such as windows in unxutils 3 and ibm i 4 in unix and unix like operating systems a system call with the same name as the command chmod provides access to the underlying access control data the command exposes the capabilities of the system call to a shell user as the need for enhanced file system permissions grew access control lists 5 were added to many file systems to augment the modes controlled via chmod the implementation of chmod bundled in gnu coreutils was written by david mackenzie and jim meyering 6 use edit although the syntax of the command varies somewhat by implementation it generally accepts either a single octal value which specifies all the mode bits on each file or a comma delimited list of symbolic specifiers which describes how to change the existing mode bits of each file the remaining arguments are a list of paths to files to be modified 7 changing permissions is only allowed for the superuser root and the owner of a file if a symbolic link is specified the target of the link has its mode bits adjusted permissions directly associated with a symbolic link file system entry are typically not used options edit optional command line options may include r recursive include contained files and subdirectories of specified directories v verbose log changed file names octal notation edit given a numeric permissions argument the chmod command treats it as an octal number a and replaces all the mode bits for each file although four digits are specified leading 0 digits can be elided 8 there are twelve standard mode bits comprising three special bits setuid setgid and sticky and three permission groups controlling access by user group and other of 3 bits each read write and exec scan each permission bit grants access if set 1 or denies access if clear 0 as an octal digit represents a 3 bit value the twelve mode bits can be represented as four octal digits chmod accepts up to four digits and uses 0 for left digits not specified as is normal for numeric representation in practice three digits are commonly specified since the special modes are rarely used and the user class is usually specified in the context of an octal digit each operation bit represents a numeric value read 4 write 2 and execute 1 the following table relates octal digit values to a class operations value octal digit permission bits rwx granted operations 7 4 2 1 rwx read write and execute 6 4 2 rw read and write 5 4 1 r x read and execute 4 4 r read only 3 2 1 wx write and execute 2 2 w write only 1 1 x execute only 0 none the command stat can report a file s permissions as octal for example stat c a findphonenumbers sh 754 the reported value 754 indicates the following permissions user class read write and execute 7 4 2 1 group class read and execute 5 4 1 others class read only 4 a code permits execution if and only if it is odd i e 1 3 5 or 7 a code permits read if and only if it is greater than or equal to 4 i e 4 5 6 or 7 a code permits write if and only if it is 2 3 6 or 7 symbolic notation edit the chmod command accepts symbolic notation that specifies how to modify the existing permissions 9 the command accepts a comma separate list of specifiers like classes operations classes map permissions to users a change specifier can select one class by including its symbol multiple by including each class s symbol with no delimiter or all classes by not specifying a symbol when using the last method the bits of the umask mask will remain unchanged 10 class specifiers include class specifiers symbol description u user file owner g group members of the file s group o others users who are neither the file s owner nor members of the file s group a all three classes same as ugo as ownership is key to access control and since the symbolic specification uses the abbreviation o some incorrectly think that it means owner when in fact it is short for others the change operators include operators symbol description add operations flags remove operations flags set the entire operations flags field grants the specified operations and denies others operations can be specified as follows operation specifiers symbol description r r ead a regular file or list a directory s contents w w rite to a file x e x ecute a regular file or recurse a directory tree x special execute selects to apply execute to directories regardless of their current permissions and apply execute to files that already have at least one execute permission granted for any class only useful with operation and usually in combination with option r for giving group or others access to a directory tree without setting execute permission on regular files which would normally happen with chmod r a rx instead use chmod r a rx s s etuid mode or s etgid mode t s t icky mode most chmod implementations support the specification of the special modes in octal but some do not which requires using the symbolic notation the ls command can report file permissions in a symbolic notation that is similar to the notation used with chmod ls l reports permissions in a notation that consists of 10 letters the first indicates the type of the file system entry such as dash for regular file and d for directory following that are three sets of three letters that indicate read write and execute permissions grouped by user group and others classes each position is either dash to indicate lack of permission or the single letter abbreviation for the permission to indicate that it s granted for example ls l findphonenumbers sh rwxr xr 1 dgerman staff 823 dec 16 15 03 findphonenumbers sh the permission specifier rwxr xr starts with a dash which indicates that findphonenumbers sh is a regular file not a directory the next three letters rwx indicate that the file can be read written and executed by the owning user dgerman the next three letters r x indicate that the file can be read and executed by members of the staff group and the last three letters r indicate that the file is read only for other users examples edit add w rite permission to the g roup class of a directory allowing users in the same group to add files ls ld dir before drwxr xr x 2 jsmitt northregion 96 apr 8 12 53 shared_dir chmod g w dir ls ld dir after drwxrwxr x 2 jsmitt northregion 96 apr 8 12 53 shared_dir remove w rite permission for a ll classes preventing anyone from writing to the file ls l ourbestreferencefile rw rw r 2 tmiller northregion 96 apr 8 12 53 ourbestreferencefile chmod a w ourbestreferencefile ls l ourbestreferencefile r r r 2 tmiller northregion 96 apr 8 12 53 ourbestreferencefile set the permissions for the u ser and g roup classes to r ead and e x ecute only with no w rite permission preventing anyone from adding files ls ld referencelib drwxr 2 ebowman northregion 96 apr 8 12 53 referencelib chmod ug rx referencelib ls ld referencelib dr xr x 2 ebowman northregion 96 apr 8 12 53 referencelib enable r ead and w rite for the u ser class while making it r ead only for g roup and others chmod u rw go r sample ls ld sample drw r r 2 oschultz warehousing 96 dec 8 12 53 sample to recursively set access for the directory docs and its contained files chmod r u w docs to set user and group for read and write only and set others for read only chmod 664 file to set user for read write and execute only and group and others for read only chmod 744 file to set the sticky bit in addition to user group and others permissions chmod 1755 file to set uid in addition to user group and others permissions chmod 4755 file to set gid in addition to user group and others permissions chmod 2755 file see also edit attrib cacls modifies access control lists chattr changes the attributes of a file chgrp changes the group of a file chown changes the owner of a file group identifier unix posix system account group number numeric value used to represent a specific group list of posix commands user identifier value identifying a user account in unix and unix like operating systems umask restricts permissions at file creation notes edit why octal rather than decimal although rarely used today during the early development of unix octal was very useful because repeating groups of 3 bits were common in the physical structure of computers at the time and these bits were easier to read and understand when encoded as octal digits just as groups of 4 bits are easier when grouped into hexadecimal digits the numeric expression of filesystem permissions in octal is one of the few remnants of this time original research references edit the modes permissions are shown when listing files in long format tutorial for chmod catcode com archived from the original on 20 may 2000 retrieved 26 august 2008 native win32 ports of some gnu utilities unxutils sourceforge net archived from the original on 9 february 2006 retrieved 9 august 2025 ibm ibm system i version 7 2 programming qshell pdf ibm archived pdf from the original on 18 september 2020 retrieved 5 september 2020 aix 5 3 system management ibm knowledge center ibm archived from the original on 4 march 2016 retrieved 30 august 2015 chmod 1 change file mode bits linux man page linux die net archived from the original on 9 january 2019 retrieved 6 january 2019 chmod man page with examples and calculator linux ss64 com ss64 com archived from the original on 12 february 2003 retrieved 12 september 2020 note that space delimited is a feature of the shell not of chmod itself this differs from the c language where the 0 prefix for octal numbers is a remnant of its early period aix 5 5 commands reference ibm knowledge center ibm archived from the original on 4 march 2016 retrieved 30 august 2015 permissions masking with umask chmod 777 octal permissions teaching idallen com archived from the original on 22 february 2020 retrieved 9 march 2020 external links edit the wikibook guide to unix has a page on the topic of commands chmod 1 change file modes freebsd general commands manual chmod 1 plan 9 programmer s manual volume 1 chmod 1 inferno general commands manual chmod manual page from gnu coreutils gnu setting permissions manual chmod win 3 0 freeware windows acl chmod converter beginners tutorial with on line live example v t e unix command line utilities and shell builtins file system cat chattr chmod chown chgrp cksum cmp cp dd du df file fuser ln ls mkdir mv pax pwd rm rmdir split tee touch type umask processes at bg crontab fg kill nice ps time user environment env exit logname mesg talk tput uname who write text processing awk basename comm csplit cut diff dirname ed ex fold head iconv join m4 more nl paste patch printf read sed sort strings tail tr troff uniq vi wc xargs shell builtins alias cd echo test unset wait searching find grep documentation man software development ar ctags lex make nm strip yacc miscellaneous bc cal dc expr lp od sleep true and false categories standard unix programs unix sus2008 utilities list v t e plan 9 command line interface programs and shell builtins file system chmod chgrp cmp cp dd du file gzip ls mkdir pwd rm split tee touch processes kill ps user environment passwd who text processing awk basename comm diff ed eqn join sed sort spell strings tail tr troff uniq wc shell builtins echo test networking ip ipconfig ip ping netstat searching grep software development ar hoc lex nm strip yacc miscellaneous bc cal fortune sleep category v t e gnu core utilities command line interface programs file system chcon chmod chown chgrp cksum cp dd df dir dircolors install ln ls mkdir mkfifo mknod mktemp mv realpath rm rmdir shred sync touch truncate vdir text utilities b2sum base32 base64 cat cksum comm csplit cut expand fmt fold head join md5sum nl numfmt od paste ptx pr sha1sum shuf sort split sum tac tail tr tsort unexpand uniq wc shell utilities arch basename chroot date dirname du echo env expr factor false groups hostid id link logname nice nohup nproc pathchk pinky printenv printf pwd readlink runcon seq sleep stat stdbuf stty tee test timeout true tty uname unlink uptime users who whoami yes retrieved from https en wikipedia org w index php title chmod oldid 1361052839 categories file system permissions operating system security standard unix programs unix file system related software unix sus2008 utilities plan 9 commands inferno operating system commands ibm i qshell commands hidden categories articles with short description short description is different from wikidata all articles that may contain original research articles that may contain original research from august 2025 use dmy dates from january 2018 this page was last edited on 25 june 2026 at 09 24 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of 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