Introduction to Unix Operating System

1. Introduction to Unix Operating System

2. Additional File System Calls Directory System Calls Today’s Agenda

3. Additional file system calls • File system calls • truncate and ftruncate • fstat, stat and lstat (struct stat) • rename (renames a file or directory) • chmod (changes permission on file/directory)

4. truncate() #include<unistd.h> int truncate( const char *path, /*pathname*/ off_t length); /*new length*/ /*Returns 0 on success and -1 on failure*/ #include<unistd.h> int truncate( int fd, /*file descriptor*/ off_t length); /*new length*/ /*Returns 0 on success and -1 on failure*/

5. Accessing and displaying file Metadata • stat(),fstat(),lstat() systam calls • These system calls helps to retrieve file meta data (inode info) like owner, modification time, access permissions etc. #include<sys/stat.h> int stat( const char *path, /*pathname*/ struct stat *buf); /*returned information*/ /*Returns 0 on success and -1 on failure*/ struct stat will store all the information which can be printed

6. Struct stat • struct stat { dev_t st_dev; /* ID of device containing file */ ino_t st_ino; /* inode number */ mode_t st_mode; /* protection */ nlink_t st_nlink; /* number of hard links */ uid_t st_uid; /* user ID of owner */ gid_t st_gid; /* group ID of owner */ dev_t st_rdev; /* device ID (if special file) */ off_t st_size; /* total size, in bytes */ blksize_t st_blksize; /* blocksize for file system I/O */ blkcnt_t st_blocks; /* number of 512B blocks allocated */ time_t st_atime; /* time of last access */ time_t st_mtime; /* time of last modification */ time_t st_ctime; /* time of last status change */ };

7. The following POSIX macros are defined to check the file type using the st_mode field: S_ISREG(m) is it a regular file? S_ISDIR(m) directory? S_ISCHR(m) character device? S_ISBLK(m) block device? S_ISFIFO(m) FIFO (named pipe)? S_ISLNK(m) symbolic link? (Not in POSIX.1-1996.) S_ISSOCK(m) socket? (Not in POSIX.1-1996.)

8. Directory System Calls • getcwd() • mkdir() • chdir() • rmdir() • opendir() • closedir() • readdir()

9. getcwd System Call • To get the current working directory in UNIX, we use the “pwd” command. • The system call behind the “pwd” command is the getcwd() call. # include<unistd.h> char *getcwd( char *buf, /* Returned pathname */ size_t bufsize /* sizeof buf */ ); /* Returns pointer to 'buf' on success and NULL on error */ bufsize should the maximum size of path. Following system call to get maximum size of path long max= pathconf(“/”,_PC_PATH_MAX);

10. A program that uses the getcwd() # include<stdio.h> # include<unistd.h> int main(void) { long max; char *buf; max= pathconf(“/”,_PC_PATH_MAX); buf=(char*)malloc(max); getcwd(buf,max); printf(“%s\n”,buf); return 0; }

11. chdir System Call(cdcommand in Unix) # include<unistd.h> int chdir( const char *path; ); /* Returns zero on success and -1 on error */ This system call changes the current working directory to that specified in “path”.

12. Make and remove dir System Call # include<sys/stat.h> intmkdir( const char *path, /* Pathname */ mode_t perms /* Permissions */ ); /* Returns 0 on success and -1 on error */ intrmdir( const char *path /* Pathname */ ); /* Returns 0 on success and -1 on error */

13. Program to make and remove directory int main(int argc,char *argv[]) { int md,rd; DIR *ds; struct dirent *dir; md = mkdir(argv[1],0777); if(md == 0) printf("%s directory is created\n",argv[1]); else printf("%s directory is not created\n",argv[1]); rd = rmdir(argv[2]); if(rd == 0) printf("%s directory is removed\n",argv[2]); else printf("%s directory is not removed\n",argv[2]); }

14. opendir and closedir System Calls # include<dirent.h> DIR* opendir( const char *path /* directory pathname */ ); /* Returns a DIR pointer or NULL on error */ # include<dirent.h> int closedir( DIR *dirp /*DIR pointer from opendir */ ); /* Returns a 0 on success or -1 on error */

15. readdir System Call and dirent structure #include <dirent.h> struct dirent *readdir( DIR *dirp /* DIR Pointer from opendir */ ); /* Returns structure or NULL on EOF or error */ struct dirent { ino_t d_ino; /* i-number */ char d_name[]; /* name */ };

16. int main(int argc,char *argv[]) { DIR *ds; struct dirent *dir; ds = opendir(argv[1]); if(ds == NULL) printf("directory %s is not opened\n",argv[1]); else printf("ds = %ld\n",ds); printf("list of files and directories\n"); while((dir = readdir(ds)) != NULL) printf("%s\n",dir->d_name); if((cld = closedir(ds)) == 0) printf("%s is successfully closed\n",argv[1]); else printf("%s is not successfully closed\n",argv[1]); } [Mayuri@localhost dirProgs]$ ./a.out /home/Mayuri/Downloads/ open the directory ds = 9236496 list of files and directories .. . SimplescalarHowto.pdf Installation_Guide_for_SimpleScalar.pdf p130-spradling.pdf /home/Mayuri/Downloads/ is successfully closed [Mayuri@localhost dirProgs]$

17. program to display the detailed directory structure (output) mayuri@atlas:~$ ./a.out dsa Directory scan of dsa lab1/ SortedSeqList.h greedyAlgos/ a.out coinset.c IntervalScheduling/ a.out dataDef.h output.txt schOps.h input.txt main.c schedulingOps.c schedulingOps.o **************DONE************ mayuri@atlas:~$

18. Exercise program • Write a program to mimic ls –l command in unix. • Write a program to display number of files in current working directory. • Write a program which performs rm –r unix command.