Working with the Unix OS

Processes I
! Shadow Password
/etc/shadow set so that only superuser can read.
The encrypted-password field is set to an asterisk.
! Group File
/etc/group
group-name:encypted-password:group-ID:user-list
BSD4.3:
System V:
can be a member of up to 16 groups at login
you change groups with the newgrp command
#include
struct group *getgrgid(int gid);
struct group *getgrnam(char *name);
struct group {
char *gr_name; /* group-name */
char *gr-passwd; /* encrypted-password */
int gr_gid; /* group-ID */
char **gr_mem; /* array of ptrs to user-list */
};
! Shells
/bin/sh Bourne shell
/bin/ksh Korne shell
/bin/csh C shell
/bin/tcsh Enhanced C shell
! Filenames
limit of 14 to 256 characters
NULL ('\0') terminates pathname
slash ('/') separates filenames
characters interpreted by shell are not recommended *, [, ], -
! Pathname
relative – path begins at current directory
absolute – starts with a slash (from root)
! File Descriptor
a small integer used to identify a file that has been opened for I/O
0 standard input
1 standard output
2 standard error
assigned by the kernel by a system call {open, creat, dup, pipe, fcntl}
! Files
#include
#include
int stat(char *pathname, struct stat *buf);
int fstat(int fildes, strut stat *buf);
struct stat {
ushort st_mode; /* file type & access perms */
ino_t st_dev; /* i-node number */
dev_t st_dev; /* ID of device containing directory entry for file */
short st_nlink; /* number of links */
ushort st_uid; /* user ID */
ushort st_gid; /* group ID */
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