faccessat2 - Linux
Overview
faccessat2 evaluates whether the calling process has the specified access to a file opened by another process. It checks the specified access and the corresponding permissions on the file.
Syntax
faccessat2(int dirfd, const char *pathname, int mode, int flag)
Options/Flags
Required Parameters
- dirfd: An integer representing the file descriptor of the directory containing the file.
- pathname: A null-terminated string specifying the path of the file to be checked.
- mode: An integer specifying the access mode to be checked. Valid options include:
F_OK
– Checks for file existence.R_OK
– Checks for read access.W_OK
– Checks for write access.X_OK
– Checks for execute access.- Logical ORs of the above values to check multiple permissions simultaneously.
Optional Parameter(s)
- flag: An integer flag that modifies the behavior of the call:
AT_EACCESS
– Check for effective access rights.AT_NO_AUTOMOUNT
– If the file is not found, do not attempt to mount it automatically.AT_SYMLINK_NOFOLLOW
– Do not follow symbolic links in the path.
Examples
Check if a file exists:
int fd = open("myfile.txt", O_RDONLY);
if (faccessat2(fd, "myfile.txt", F_OK, 0) == 0) {
printf("myfile.txt exists.\n");
} else {
printf("myfile.txt does not exist.\n");
}
Check if a file is readable:
if (faccessat2(fd, "myfile.txt", R_OK, 0) == 0) {
printf("myfile.txt is readable.\n");
} else {
printf("myfile.txt is not readable.\n");
}
Check if a symbolic link can be executed:
if (faccessat2(fd, "mylink", X_OK, AT_SYMLINK_NOFOLLOW) == 0) {
printf("mylink can be executed.\n");
} else {
printf("mylink cannot be executed.\n");
}
Common Issues
- Ensure the file descriptor is valid and the file is accessible to the calling process.
- Check that the
pathname
is correct and does not contain any errors. - If
AT_EACCESS
is used, make sure the calling process has the proper privileges to check the effective access rights.
Integration
Combine with ls: List files and check their access permissions using faccessat2:
ls -l | while read line; do
file=$(echo $line | cut -d' ' -f11)
fd=$(echo $line | cut -d' ' -f1)
if [ -z "$file" ] || [ ! -d "$file" ]; then continue; fi
if [ $(faccessat2 $fd $file X_OK) -eq 0 ]; then
echo "$file is executable."
else
echo "$file is not executable."
fi
done
Related Commands
- access: Checks the access rights of a file for the current process.
- stat: Obtains detailed information about a file.
- open: Opens a file and returns a file descriptor.
- close: Closes a file descriptor.