Module

The Etc module provides access to information typically stored in files in the /etc directory on Unix systems.

The information accessible consists of the information found in the /etc/passwd and /etc/group files, plus information about the system's temporary directory (/tmp) and configuration directory (/etc).

The Etc module provides a more reliable way to access information about the logged in user than environment variables such as +$USER+.

Example:

require 'etc'

login = Etc.getlogin
info = Etc.getpwnam(login)
username = info.gecos.split(/,/).first
puts "Hello #{username}, I see your login name is #{login}"

Note that the methods provided by this module are not always secure. It should be used for informational purposes, and not for security.

All operations defined in this module are class methods, so that you can include the Etc module into your class.


Constants


Group

Group is a Struct that is only available when compiled with HAVE_GETGRENT.

The struct contains the following members:

name

contains the name of the group as a String.

passwd

contains the encrypted password as a String. An 'x' is returned if password access to the group is not available; an empty string is returned if no password is needed to obtain membership of the group.

Must be compiled with HAVE_STRUCT_GROUP_GR_PASSWD.

gid

contains the group's numeric ID as an integer.

mem

is an Array of Strings containing the short login names of the members of the group.

Passwd

Passwd is a Struct that contains the following members:

name

contains the short login name of the user as a String.

passwd

contains the encrypted password of the user as a String. an 'x' is returned if shadow passwords are in use. An '*' is returned if the user cannot log in using a password.

uid

contains the integer user ID (uid) of the user.

gid

contains the integer group ID (gid) of the user's primary group.

dir

contains the path to the home directory of the user as a String.

shell

contains the path to the login shell of the user as a String.

The following members below are optional, and must be compiled with special flags:

gecos

contains a longer String description of the user, such as a full name. Some Unix systems provide structured information in the gecos field, but this is system-dependent. must be compiled with HAVE_STRUCT_PASSWD_PW_GECOS

change

password change time(integer) must be compiled with HAVE_STRUCT_PASSWD_PW_CHANGE

quota

quota value(integer) must be compiled with HAVE_STRUCT_PASSWD_PW_QUOTA

age

password age(integer) must be compiled with HAVE_STRUCT_PASSWD_PW_AGE

class

user access class(string) must be compiled with HAVE_STRUCT_PASSWD_PW_CLASS

comment

comment(string) must be compiled with HAVE_STRUCT_PASSWD_PW_COMMENT

expire

account expiration time(integer) must be compiled with HAVE_STRUCT_PASSWD_PW_EXPIRE

No documentation available

Class Methods


Returns system configuration variable using confstr().

name should be a constant under Etc which begins with CS_.

The return value is a string or nil. nil means no configuration-defined value. (confstr() returns 0 but errno is not set.)

Etc.confstr(Etc::CS_PATH) #=> "/bin:/usr/bin"

# GNU/Linux
Etc.confstr(Etc::CS_GNU_LIBC_VERSION) #=> "glibc 2.18"
Etc.confstr(Etc::CS_GNU_LIBPTHREAD_VERSION) #=> "NPTL 2.18"

Ends the process of scanning through the /etc/group file begun by ::getgrent, and closes the file.

Ends the process of scanning through the /etc/passwd file begun with ::getpwent, and closes the file.

Returns an entry from the /etc/group file.

The first time it is called it opens the file and returns the first entry; each successive call returns the next entry, or nil if the end of the file has been reached.

To close the file when processing is complete, call ::endgrent.

Each entry is returned as a Group struct

Returns information about the group with specified integer group_id, as found in /etc/group.

The information is returned as a Group struct.

See the unix manpage for getgrgid(3) for more detail.

Example:

Etc.getgrgid(100)
#=> #<struct Etc::Group name="users", passwd="x", gid=100, mem=["meta", "root"]>

Returns information about the group with specified name, as found in /etc/group.

The information is returned as a Group struct.

See the unix manpage for getgrnam(3) for more detail.

Example:

Etc.getgrnam('users')
#=> #<struct Etc::Group name="users", passwd="x", gid=100, mem=["meta", "root"]>

Returns the short user name of the currently logged in user. Unfortunately, it is often rather easy to fool ::getlogin.

Avoid ::getlogin for security-related purposes.

If ::getlogin fails, try ::getpwuid.

See the unix manpage for getpwuid(3) for more detail.

e.g.

Etc.getlogin -> 'guest'

Returns an entry from the /etc/passwd file.

The first time it is called it opens the file and returns the first entry; each successive call returns the next entry, or nil if the end of the file has been reached.

To close the file when processing is complete, call ::endpwent.

Each entry is returned as a Passwd struct.

Returns the /etc/passwd information for the user with specified login name.

The information is returned as a Passwd struct.

See the unix manpage for getpwnam(3) for more detail.

Example:

Etc.getpwnam('root')
#=> #<struct Etc::Passwd name="root", passwd="x", uid=0, gid=0, gecos="root",dir="/root", shell="/bin/bash">

Returns the /etc/passwd information for the user with the given integer uid.

The information is returned as a Passwd struct.

If uid is omitted, the value from Passwd[:uid] is returned instead.

See the unix manpage for getpwuid(3) for more detail.

Example:

Etc.getpwuid(0)
#=> #<struct Etc::Passwd name="root", passwd="x", uid=0, gid=0, gecos="root",dir="/root", shell="/bin/bash">

Provides a convenient Ruby iterator which executes a block for each entry in the /etc/group file.

The code block is passed an Group struct.

See ::getgrent above for details.

Example:

require 'etc'

Etc.group {|g|
  puts g.name + ": " + g.mem.join(', ')
}

Returns the number of online processors.

The result is intended as the number of processes to use all available processors.

This method is implemented using:

  • sched_getaffinity(): Linux

  • sysconf(_SC_NPROCESSORS_ONLN): GNU/Linux, NetBSD, FreeBSD, OpenBSD, DragonFly BSD, OpenIndiana, Mac OS X, AIX

Example:

require 'etc'
p Etc.nprocessors #=> 4

The result might be smaller number than physical cpus especially when ruby process is bound to specific cpus. This is intended for getting better parallel processing.

Example: (Linux)

linux$ taskset 0x3 ./ruby -retc -e "p Etc.nprocessors"  #=> 2

Provides a convenient Ruby iterator which executes a block for each entry in the /etc/passwd file.

The code block is passed an Passwd struct.

See ::getpwent above for details.

Example:

require 'etc'

Etc.passwd {|u|
  puts u.name + " = " + u.gecos
}

Resets the process of reading the /etc/group file, so that the next call to ::getgrent will return the first entry again.

Resets the process of reading the /etc/passwd file, so that the next call to ::getpwent will return the first entry again.

Returns system configuration variable using sysconf().

name should be a constant under Etc which begins with SC_.

The return value is an integer or nil. nil means indefinite limit. (sysconf() returns -1 but errno is not set.)

Etc.sysconf(Etc::SC_ARG_MAX) #=> 2097152
Etc.sysconf(Etc::SC_LOGIN_NAME_MAX) #=> 256

Returns system configuration directory.

This is typically “/etc”, but is modified by the prefix used when Ruby was compiled. For example, if Ruby is built and installed in /usr/local, returns “/usr/local/etc” on other platforms than Windows. On Windows, this always returns the directory provided by the system.

Returns system temporary directory; typically “/tmp”.

Returns the system information obtained by uname system call.

The return value is a hash which has 5 keys at least:

:sysname, :nodename, :release, :version, :machine

Example:

require 'etc'
require 'pp'

pp Etc.uname
#=> {:sysname=>"Linux",
#    :nodename=>"boron",
#    :release=>"2.6.18-6-xen-686",
#    :version=>"#1 SMP Thu Nov 5 19:54:42 UTC 2009",
#    :machine=>"i686"}