Open System Services System Calls Reference Manual (G06.28+, H06.05+)

System Functions (a - d) access(2)

NAME

access - Determines the accessibility of a ﬁle

LIBRARY

G-series native OSS processes: system library

H-series OSS processes: implicit libraries

SYNOPSIS

#include <unistd.h>

int access(

const char *path,

int access_mode);

PARAMETERS

path Points to the ﬁle pathname. When the path parameter refers to a symbolic link,

the access() function returns information about the ﬁle pointed to by the sym-

bolic link.

Permission to access all components of the path parameter is determined by

using a real user ID instead of an effective user ID, and by using a real group ID

instead of an effective group ID.

access_mode Speciﬁes the type of access. The bit pattern contained in the access_mode

parameter is constructed by a logical OR of values from the following list:

F_OK Checks to see whether the ﬁle exists.

R_OK Checks read permission.

W_OK Checks write permission.

X_OK Checks execute (search) permission.

DESCRIPTION

The access() function checks the accessibility of a ﬁle speciﬁed by a pathname.

Only access bits are checked. A directory can be indicated as writable by access(), but an

attempt to open it for writing could fail (although ﬁles can be created there).

To override the ﬁle access control mechanism, a process must have a user ID of the super ID.

Access Control Lists (ACLs)

Read, write, and execute/search permissions are checked against the ACL for the ﬁle. |

To determine the permission granted to the real user ID (RUID) and real group ID (RGID) of the |

accessing process, the access() function checks these things in the ACL, in order:

1. If the RUID of the process is the same as the owner of the ﬁle, grant the permissions |

speciﬁed in the user:: entry. Otherwise, continue to the next check.

2. If the RUID matches the UID speciﬁed in one of the additional user:uid: entries, grant |

the permissions speciﬁed in that entry, bitwise-ANDed with the permissions speciﬁed in |

the class entry. Otherwise, continue to the next check.

3. If the RGID or a supplementary GID of the process matches the owning GID of the ﬁle |

or one of the GIDs speciﬁed in any additional group:gid: entries, grant the permissions |

speciﬁed in the class entry bitwise-ANDed with the result of bitwise-ORing together all |

of the permissions in all matching group entries. Otherwise, continue to the next check.

4. Otherwise, grant the permissions speciﬁed in the other entry. |

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