GETUSERSHELL(3) Linux Programmer's Manual GETUSERSHELL(3)

getusershell, setusershell, endusershell - get permitted user shells

#include <unistd.h>
char *getusershell(void);
void setusershell(void);
void endusershell(void);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getusershell(), setusershell(), endusershell():

Since glibc 2.21:
    _DEFAULT_SOURCE
In glibc 2.19 and 2.20:
    _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
Up to and including glibc 2.19:
    _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

The getusershell() function returns the next line from the file /etc/shells, opening the file if necessary. The line should contain the pathname of a valid user shell. If /etc/shells does not exist or is unreadable, getusershell() behaves as if /bin/sh and /bin/csh were listed in the file.

The setusershell() function rewinds /etc/shells.

The endusershell() function closes /etc/shells.

The getusershell() function returns NULL on end-of-file.

/etc/shells

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
getusershell (), setusershell (), endusershell () Thread safety MT-Unsafe

4.3BSD.

shells(5)

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2021-03-22 GNU