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 | man pages section 2: System Calls Oracle Solaris 11 Information Library |
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| man pages section 2: System Calls Oracle Solaris 11 Information Library |
- change access permission mode of file
#include <sys/stat.h>intchmod(const char *path,mode_tmode);
intfchmod(intfildes,mode_tmode);
int fchmodat(intfd, const char *path, mode_tmode, intflag);
Thechmod() andfchmod() functions set the access permission portion of themode of the file whose name is given bypath or referencedby the open file descriptorfildes to the bit pattern contained inmode. Access permission bits are interpreted as follows:
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Modes are constructed by the bitwise OR operation of the access permissionbits.
The effective user ID of the process must match the owner ofthe file or the process must have the appropriate privilege to changethe mode of a file.
If the process is not a privileged process and the file isnot a directory, mode bit 01000 (save text image on execution) iscleared.
If neither the process is privileged nor the file's group is amember of the process's supplementary group list, and the effective groupID of the process does not match the group ID of thefile, mode bit 02000 (set group ID on execution) is cleared.
If a directory is writable and hasS_ISVTX (the sticky bit) set,files within that directory can be removed or renamed only if oneor more of the following is true (seeunlink(2) andrename(2)):
the user owns the file
the user owns the directory
the file is writable by the user
the user is a privileged user
If a regular file is not executable and hasS_ISVTX set, thefile is assumed to be a swap file. In this case, thesystem's page cache will not be used to hold the file's data.If theS_ISVTX bit is set on any other file, the resultsare unspecified.
If a directory has the set group ID bit set, a givenfile created within that directory will have the same group IDas the directory. Otherwise, the newly created file's group ID willbe set to the effective group ID of the creating process.
If the mode bit 02000 (set group ID on execution) is setand the mode bit 00010 (execute or search by group) is notset, mandatory file/record locking will exist on a regular file, possibly affectingfuture calls toopen(2),creat(2),read(2), andwrite(2) on this file.
Iffildes references a shared memory object,fchmod() need only affect theS_IRUSR,S_IRGRP,S_IROTH,S_IWUSR,S_IWGRP,S_IWOTH,S_IXUSR,S_IXGRP, andS_IXOTH file permissionbits.
Iffildes refers to a socket,fchmod() does not fail but noaction is taken.
Iffildes refers to a stream that is attached to an objectin the file system name space withfattach(3C), thefchmod() call performs noaction and returns successfully.
Upon successful completion,chmod() andfchmod() mark for update thest_ctime fieldof the file.
Thefchmodat() function is equivalent tochmod() except in the case wherepath specifies a relative path. In this case the file to bechanged is determined relative to the directory associated with the file descriptorfd instead of the current working directory. If the file descriptor was openedwithoutO_SEARCH, the function checks whether directory searches are permitted using thecurrent permissions of the directory underlying the file descriptor. If the filedescriptor was opened withO_SEARCH, the function does notperform the check.
Values for flag are constructed by a bitwise-inclusive OR of flags fromthe following list, defined in<fcntl.h>
Ifpath names a symbolic link, then the mode of the symbolic link is changed.
Iffchmodat() is passed the special valueAT_FDCWD in thefd parameter,the current working directory is used. Ifflag is also 0, thebehavior shall be identical to a call tochmod().
Upon successful completion,0 is returned. Otherwise,-1 is returned, the filemode is unchanged, anderrno is set to indicate the error.
Thechmod(),fchmod(), andfchmodat() functions will fail if:
The effective user ID does not match the owner of the file and the process does not have appropriate privilege.
The {PRIV_FILE_OWNER} privilege overrides constraints on ownership when changing permissions on a file.
The {PRIV_FILE_SETID} privilege overrides constraints on ownership when adding the setuid or setgid bits to an executable file or a directory. When adding the setuid bit to a root owned executable, additional restrictions apply. Seeprivileges(5).
The file referred to bypath resides on a read-only file system.
Thechmod() andfchmod() functions will fail if:
An I/O error occurred while reading from or writing to the file system.
Thechmod() andfchmodat()functions will fail if:
Search permission is denied on a component of the path prefix ofpath. The privilege {FILE_DAC_SEARCH} overrides file permissions restrictions in that case.
A loop exists in symbolic links encountered during the resolution of thepath argument.
The length of thepath argument exceedsPATH_MAX, or the length of apath component exceedsNAME_MAX while_POSIX_NO_TRUNC is in effect.
Either a component of the path prefix or the file referred to bypath does not exist or is a null pathname.
A component of the prefix ofpath is not a directory.
Thechmod() function will fail if:
Thepath argument points to an illegal address.
Thefildes argument points to a remote machine and the link to that machine is no longer active.
Thefchmod() function will fail if:
Thefildes argument is not an open file descriptor
Thepath argument points to a remote machine and the link to that machine is no longer active.
Thefchmodat() function will fail if:
fd was not opened withO_SEARCH and the permissions of the directory underlyingfd do not permit directory searches.
Thepath argument does not specify an absolute path and thefd argument is neitherAT_FDCWD nor a valid file descriptor open for reading or searching.
Thechmod(),fchmod(), andfchmodat() functions may fail if:
A signal was caught during execution of the function.
The value of themode argument is invalid.
Thechmod() andfchmodat() functions may fail if:
More than {SYMLOOP_MAX} symbolic links were encountered during the resolution of thepath argument.
As a result of encountering a symbolic link in resolution of thepath argument, the length of the substituted pathname strings exceeds {PATH_MAX}.
Thefchmod() function may fail if:
Thefildes argument refers to a pipe and the system disallows execution of this function on a pipe.
Thefchmodat() function may fail if:
The value of theflag argument is invalid
Thepath argument is not an absolute path andfd is neitherAT_FDCWD nor a file descriptor associated with a directory
TheAT_SYMLINK_NOFOLLOW bit is set in theflag argument,path names a symbolic link, and the system does not support changing the mode of a symbolic link.
Example 1 Set Read Permissions for User, Group, and Others
The following example sets read permissions for the owner, group, and others.
#include <sys/stat.h>const char *path;...chmod(path, S_IRUSR|S_IRGRP|S_IROTH);
Example 2 Set Read, Write, and Execute Permissions for the Owner Only
The following example sets read, write, and execute permissions for the owner,and no permissions for group and others.
#include <sys/stat.h>const char *path;...chmod(path, S_IRWXU);
Example 3 Set Different Permissions for Owner, Group, and Other
The following example sets owner permissions for CHANGEFILE to read, write, andexecute, group permissions to read and execute, and other permissions to read.
#include <sys/stat.h>#define CHANGEFILE "/etc/myfile" ...chmod(CHANGEFILE, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH);
Example 4 Set and Checking File Permissions
The following example sets the file permission bits for a file named/home/cnd/mod1, then calls thestat(2) function to verify the permissions.
#include <sys/stat.h>int status;struct stat buffer...chmod("home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH);status = stat("home/cnd/mod1", &buffer;);Ifchmod() orfchmod() is used to change the file group ownerpermissions on a file with non-trivial ACL entries, only the ACL maskis set to the new permissions and the group owner permission bitsin the file's mode field (defined inmknod(2)) are unchanged. Anon-trivial ACL entry is one whose meaning cannot be represented in thefile's mode field alone. The new ACL mask permissions might change theeffective permissions for additional users and groups that have ACL entries onthe file.
Seeattributes(5) for descriptions of the following attributes:
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chmod(1),chown(2),creat(2),fcntl(2),mknod(2),open(2),read(2),rename(2),stat(2),write(2),fattach(3C),mkfifo(3C),stat.h(3HEAD),attributes(5),privileges(5),standards(5)
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