 | Password File
 | The password file contains the important information of all the users
the system knows. |
| The format of the password file is described in /etc/passwd. |
| Let's take a look at the /etc/passwd and /etc/shadow. |
| A typical line is as follows.
msql:x:36:36:Mini SQL Database Manager:/var/lib/msql:/bin/sh |
| The entries in the /etc/passwd contains the following. The
fields are separated by colon ':'.
 | symbolic user name |
| optional encrypted passwd
| This is a 13-char string converted from the actual user
password |
|
| user id |
| group id |
| comment |
| user home directory |
| user login in shell |
|
| Programming interface
| We now write a program to read the information in the /etc/passwd
file.
| This program uses getpwuid
to access the passwd structure by uid. |
| We can also uses getpwnam to
access the same data structure by name. |
|
| We now write a program to access the passwd information of all
users.
| This program will be based on the implementation of getpwnam
in the textbook. |
| There are three functions to use. They are much like open,
read and close a file.
| setpwent
| Start reading of the passwd structures. |
|
| getpwent
| Sequentially read the he passwd structures. |
|
| endpwent
| Ends the reading. |
|
|
|
|
|
| Group File
| The /etc/group file contains all the information about the groups in a
UNIX system. |
| The format of the password file is described in /etc/group. |
| A typical group line is like.
audio:x:29: |
| The group file contains the following information.
| Symbolic name of the group. |
| The group password |
| The group is. |
| Comments. |
|
| The programming interface
|
| Now we extend our ls to print user id and group id in symbolic form.
| First we use stat to obtain the user id and group id of the file. |
| Then we use getpwuid to obtain
the symbolic form of the user name. |
| Then we use getgrgid to obtain
the symbolic form of the group name. |
|
|
| Login Accounting File
| The file /var/run/utmp contains the
information of current login users. |
| The file /var/log/wtmp contains the
information of all login records. |
| These two files share a common data structure that describes the login
information.
| TTY line
| From where the connection was made. |
|
| The user login name |
| The login in/out time. |
|
| During login a record is append to both record files, and during
logout the same entry is erased from utmp, but a new record is appended
to wtmp to indicate the logout event. |
| The command who reads utmp and reports
the information. |
|
| System Information
| uname
| Obtain the system information, including the following.
| The name of the system |
| The name of this node |
| The release number |
| The version number |
| The hardware type |
|
|
| gethostname
| The name of this machine. |
|
|
| File System Table File
|
| Time and Date
| The time time routine reports the time
of the system.
| The time is measured as the elapsed number of second since January
1st, 1970. |
| The time is kept in UTC. |
|
| One can also provide storage for the time routine to place the retuen
value, |
| The tm structure is a more useful form to represent the date and the
time.
| gmtime
| Convert the return value of time into tm structure according
to UTC. |
|
| localtime
| Convert the return value of time into tm structure according
to local time. |
|
| asctime
| Convert a tm into an ASCII string. |
|
| ctime
| Convert the return value of time directly into a ASCII string. |
|
| strftime
| Convert a tm structure into a formatted string. |
|
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