diff options
Diffstat (limited to 'man2/access.2')
| -rw-r--r-- | man2/access.2 | 69 |
1 files changed, 45 insertions, 24 deletions
diff --git a/man2/access.2 b/man2/access.2 index 3f492d2..7e60a33 100644 --- a/man2/access.2 +++ b/man2/access.2 @@ -20,7 +20,7 @@ .\" Modified 2004-06-23 by Michael Kerrisk .\" 2007-06-10, mtk, various parts rewritten, and added BUGS section. .\" -.TH access 2 2023-03-30 "Linux man-pages 6.05.01" +.TH access 2 2024-01-01 "Linux man-pages 6.7" .SH NAME access, faccessat, faccessat2 \- check user's permissions for a file .SH LIBRARY @@ -29,30 +29,30 @@ Standard C library .SH SYNOPSIS .nf .B #include <unistd.h> -.PP +.P .BI "int access(const char *" pathname ", int " mode ); -.PP +.P .BR "#include <fcntl.h>" " /* Definition of " AT_* " constants */" .B #include <unistd.h> -.PP +.P .BI "int faccessat(int " dirfd ", const char *" pathname ", int " \ mode ", int " flags ); /* But see C library/kernel differences, below */ -.PP +.P .BR "#include <fcntl.h>" " /* Definition of " AT_* " constants */" .BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */" .B #include <unistd.h> -.PP +.P .B int syscall(SYS_faccessat2, .BI " int " dirfd ", const char *" pathname ", int " mode \ ", int " flags ); .fi -.PP +.P .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE -.PP +.P .BR faccessat (): .nf Since glibc 2.10: @@ -67,7 +67,7 @@ checks whether the calling process can access the file If .I pathname is a symbolic link, it is dereferenced. -.PP +.P The .I mode specifies the accessibility check(s) to be performed, @@ -81,7 +81,7 @@ tests for the existence of the file. .BR R_OK ", " W_OK ", and " X_OK test whether the file exists and grants read, write, and execute permissions, respectively. -.PP +.P The check is done using the calling process's .I real UID and GID, rather than the effective IDs as is done when @@ -92,7 +92,7 @@ Similarly, for the root user, the check uses the set of permitted capabilities rather than the set of effective capabilities; and for non-root users, the check uses an empty set of capabilities. -.PP +.P This allows set-user-ID programs and capability-endowed programs to easily determine the invoking user's authority. In other words, @@ -105,7 +105,7 @@ read/write/execute this file?", which gives set-user-ID programs the possibility to prevent malicious users from causing them to read files which users shouldn't be able to read. -.PP +.P If the calling process is privileged (i.e., its real UID is zero), then an .B X_OK @@ -116,7 +116,7 @@ is enabled for any of the file owner, group, or other. operates in exactly the same way as .BR access (), except for the differences described here. -.PP +.P If the pathname given in .I pathname is relative, then it is interpreted relative to the directory @@ -126,7 +126,7 @@ referred to by the file descriptor the calling process, as is done by .BR access () for a relative pathname). -.PP +.P If .I pathname is relative and @@ -138,13 +138,13 @@ then is interpreted relative to the current working directory of the calling process (like .BR access ()). -.PP +.P If .I pathname is absolute, then .I dirfd is ignored. -.PP +.P .I flags is constructed by ORing together zero or more of the following values: .TP @@ -155,12 +155,33 @@ By default, uses the real IDs (like .BR access ()). .TP +.BR AT_EMPTY_PATH " (since Linux 5.8)" +If +.I pathname +is an empty string, operate on the file referred to by +.I dirfd +(which may have been obtained using the +.BR open (2) +.B O_PATH +flag). +In this case, +.I dirfd +can refer to any type of file, not just a directory. +If +.I dirfd +is +.BR AT_FDCWD , +the call operates on the current working directory. +This flag is Linux-specific; define +.B _GNU_SOURCE +to obtain its definition. +.TP .B AT_SYMLINK_NOFOLLOW If .I pathname is a symbolic link, do not dereference it: instead return information about the link itself. -.PP +.P See .BR openat (2) for an explanation of the need for @@ -346,20 +367,20 @@ interval between checking and opening the file to manipulate it. a safer alternative would be to temporarily switch the process's effective user ID to the real ID and then call .BR open (2).) -.PP +.P .BR access () always dereferences symbolic links. If you need to check the permissions on a symbolic link, use .BR faccessat () with the flag .BR AT_SYMLINK_NOFOLLOW . -.PP +.P These calls return an error if any of the access types in .I mode is denied, even if some of the other access types in .I mode are permitted. -.PP +.P A file is accessible only if the permissions on each of the directories in the path prefix of .I pathname @@ -367,7 +388,7 @@ grant search (i.e., execute) access. If any directory is inaccessible, then the .BR access () call fails, regardless of the permissions on the file itself. -.PP +.P Only access bits are checked, not the file type or contents. Therefore, if a directory is found to be writable, it probably means that files can be created in the directory, @@ -375,7 +396,7 @@ and not that the directory can be written as a file. Similarly, a DOS file may be reported as executable, but the .BR execve (2) call will still fail. -.PP +.P These calls may not work correctly on NFSv2 filesystems with UID mapping enabled, because UID mapping is done on the server and hidden from the client, @@ -401,7 +422,7 @@ Starting with glibc 2.33, the wrapper function avoids this bug by making use of the .BR faccessat2 () system call where it is provided by the underlying kernel. -.PP +.P In Linux 2.4 (and earlier) there is some strangeness in the handling of .B X_OK tests for superuser. @@ -424,7 +445,7 @@ returns 0 for such files. .\" This behavior appears to have been an implementation accident. Early Linux 2.6 (up to and including Linux 2.6.3) also behaved in the same way as Linux 2.4. -.PP +.P Before Linux 2.6.20, these calls ignored the effect of the .B MS_NOEXEC |