The Hacker's Encyclopedia 1998

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Subj : General UNIX reference guide ──────────────────────────────────────────────────────────────────────────────── Below you will find a quick reference on basic navigation within the UNIX environment. The target audience is introductory level UNIX. Any switches described are straight from the man pages. Previous experience operating from a command line interface like MS-DOS is assumed. First you need access to a UNIX box or a shell account. For the purpose of my audience I will assume shell in my examples, though there is no difference. You'll find the directory structure strikingly similiar to DOS on appearance. The big difference you'll see right off is the use of / instead of \ when seperating directories. Besides that, individual files have permissions instead of attributes. Another thing to consider and know is that UNIX is case sensitive, myfile.doc and Myfile.doc are considered two different files. You can get further information on any command in UNIX by typing man <command>. Changing directories: Same as in DOS, cd <target dir>. For example, to switch to a directory called "mydir" off the root I would type cd /mydir (using the begining / to signafy from the start of everything). You can use cd . - to change to the root dir (remember, UNIX has permissions, you may not have permission to do this or to list the contents). cd .. will change up a step on the directory tree, for example if you are currently in /home/mydir and you want to go to /home, then cd .. will get you there. Listing the Contents of a directory: Instead of using dir, like in DOS, in UNIX use ls. Using ls alone lists the files like the DOS command dir /w would. A common way is to use ls -l, which will show you the file permissions, size, and other information. You see the permissions as letters: r the file is readable; w the file is writable; x the file is executable; - the indicated permission is not granted. Below you will find all the switches for ls and what each does: -a List all entries; in the absence of this option, entries whose names begin with a `.' are not listed (except for the super-user, for whom ls, but not /usr/5bin/ls, normally prints even files that begin with a `.'). -A (ls only) Same as -a, except that `.' and `..' are not listed. -c Use time of last edit (or last mode change) for sorting or printing. -C Force multi-column output, with entries sorted down the columns; for ls, this is the default when output is to a terminal. -d If argument is a directory, list only its name (not its contents); often used with -l to get the status of a directory. -f Force each argument to be interpreted as a directory and list the name found in each slot. This option turns off -l, -t, -s, and -r, and turns on -a; the order is the order in which entries appear in the directory. -F Mark directories with a trailing slash (`/'), execut- able files with a trailing asterisk (`*'), symbolic links with a trailing at-sign (`@'), and AF_UNIX address family sockets with a trailing equals sign -g For ls, show the group ownership of the file in a long output. For /usr/5bin/ls, print a long listing, the same as -l, except that the owner is not printed. -i For each file, print the i-number in the first column of the report. -l List in long format, giving mode, number of links, owner, size in bytes, and time of last modification for each file. If the file is a special file the size field will instead contain the major and minor device numbers. If the time of last modification is greater than six months ago, it is shown in the format `month date year'; files modified within six months show `month date time'. If the file is a symbolic link the pathname of the linked-to file is printed preceded by `->'. /usr/5bin/ls will print the group in addition to the owner. -L If argument is a symbolic link, list the file or direc- tory the link references rather than the link itself. -q Display non-graphic characters in filenames as the character ?; for ls, this is the default when output is to a terminal. -r Reverse the order of sort to get reverse alphabetic or oldest first as appropriate. -R Recursively list subdirectories encountered. -s Give size of each file, including any indirect blocks used to map the file, in kilobytes (ls) or 512-byte blocks (/usr/5bin/ls). -t Sort by time modified (latest first) instead of by name. -u Use time of last access instead of last modification for sorting (with the -t option) and/or printing (with the -l option). -1 (ls only) Force one entry per line output format; this is the default when output is not to a terminal. SYSTEM V OPTIONS -b Force printing of non-graphic characters to be in the octal \ddd notation. -m Stream output format; the file names are printed as a list separated by commas, with as many entries as pos- sible printed on a line. -n The same as -l, except that the owner's UID and group's GID numbers are printed, rather than the associated character strings. -o The same as -l, except that the group is not printed. -p Put a slash (`/') after each filename if that file is a directory. -x Multi-column output with entries sorted across rather than down the page. Copying and Moving Files To copy a file use cp, cp <source> <target>. To copy the file myfile.txt to another directory from the current directory you would type (without the ") "cp myfile.txt /home/mydir/myfile.txt". cp switches: -i Interactive. Prompt for confirmation whenever the copy would overwrite an existing file. A y in answer con- firms that the copy should proceed. Any other answer prevents cp from overwriting the file. -p Preserve. Duplicate not only the contents of the ori- ginal file or directory, but also the modification time and permission modes. -r -R Recursive. If any of the source files are directories, copy the directory along with its files (including any subdirectories and their files); the destination must be a directory. To move a file type mv <source> <target>, see the example above and switch mv with cp. To rename a file use the mv command. To rename myfile.txt to yourfile.txt type "mv myfile.txt yourfile.txt". mv switches: - Interpret all the following arguments to mv as file names. This allows file names starting with minus. -f Force. Override any mode restrictions and the -i option. The -f option also suppresses any warning mes- sages about modes which would potentially restrict overwriting. -i Interactive mode. mv displays the name of the file or directory followed by a question mark whenever a move would replace an existing file or directory. If you type a line starting with y, mv moves the specified file or directory, otherwise mv does nothing with that file or directory. To delete a file use rm. Careful with rm!!! We all shoot ourselves in the foot with this one once in a while, be especially careful if you are running from root as to what directory you are in before typing rm -f *...we all think we are in another directory when that one first bites us. rm -rf * is worse, but you'd have to be really ignorant to type that by accident. The switches for rm are as follows: -f Attempt to remove files without displaying permissions, asking questions or reporting errors. -i Ask whether to delete each file, and, under -r, whether to examine each directory. Sometimes called the interactive option. -r Recursively delete the contents of a directory, its subdirectories, and the directory itself. Making and Deleting Directories: To make a directory use mkdir. To remove one use rmdir. Setting Permissions: UNIX has file and directory permissions. You can assign and remove the ability for others to read, write, or even see specific files or directories. To set and change these permissions we use chmod <mode> <filename>. You see permissions in an ls -l and they look something like this: -rwxr-x--- 1 root 871 Sep 30 15:08 foo.sh drwxr-x--- 1 root 1024 Sep 30 15:08 mydir After the first letter (signafying a directory or file, the letters are grouped in threes ((r)ead, (w)rite, (x)ecute) for owner, group, other. chmod assigns numbers to each as follows: Owner: r - 400 w - 200 x - 100 Group: r - 40 w - 20 x - 10 Other: r - 4 w - 2 x - 1 So if I wanted the owner (chances are you, unless your administering a server) of the file only to be able do do everything with it and everyone else not to be able to do anything then yoy want the permissions to look like this: -rwx------ This means you are using only the owners set of numbers, so add them up... 400+200+100 = 700 so chmod 700 myfile. Say you want to be able to do everything to your file, but you also want to give a certain group of people the ability to read it, but not write to it. That means you want the permissions to look like this: -rwxr----- So use only those numbers and add them: 400+200+100+40 = 740 So, chmod 740 myfile get it? good. Some common settings: rwx------ -> 700 - only you have permissions rwxr--r-- -> 744 rwxrw-r-- -> 764 rwxrwx--- -> 770 rwxr-xr-x -> 755 - common web setting That should give you some of the basics for working in UNIX. I will continue with this series as I have time. The next one will be on using a default editor like vi, using ftp, and some other items. I am posting these in the interest of rebuilding 2600 into a group for more than just spam and other "l33t" crap! This was once a great group, I remember (been in the field for over 15 years), now it is laughable. I will also be answering posts in here when I have the time, been doing it for a little while now anyway, I have no sig at all...why waste the space... I post from a number of different accounts, but really don't care about who knows my identity...ask and I'll tell you. I just use a false email address so that my mailbox doesn't fill up with crap. I offer only information that I think others may find useful, from newbies on up, I will not respond to flames, challenges, can-i-crack-this, who's "l33ter", or any posts with too many z's in them ;) I only think that contributes to the degradation of the group. If someone finds what I say to be inacurate, or wishes to expand upon it...feel free to say so in an intelligent manner. If you find fault with my grammer or spelling...tough...I don't get paid for that...I get paid for my systems knowledge, besides I intentionally mistype some words all the time...for a reason. In short, lets have an intelligent well thought out discussion, not a flamefest.