2.1/2.2 系统目录结构
ls命令可以列写目录，可以看一下根目录下的内容。
[root@lhy ~]# ls /
bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
root用户的家目录就在/root/
[root@lhy ~]# ls /root
anaconda-ks.cfg openscap_data
家目录用于存储用户的配置文件和普通文件，比如
[root@lhy ~]# ls /root/.ssh/authorized_keys
/root/.ssh/authorized_keys
如果我希望通过ssh连接一个普通的非root用户，那么就需要把这个配置文件（公钥）放置在对应用户的家目录里（/etc/ssh/sshd_config文件规定的）。比如，新建一个用户lhy01，这个配置文件就需要放置在/home/lhy01/下，这个目录在创建用户时候会自动创建。
[root@lhy ~]# useradd lhy01
[root@lhy ~]# ls /home/
lhy01
[root@lhy ~]# ls /home/lhy01/ -a
. .. .bash_logout .bash_profile .bashrc
想查看一个目录有什么子目录，可以用tree命令。如果没有安装可以用yum安装。
[root@lhy ~]# yum install tree -y
Loaded plugins: fastestmirror
base | 3.6 kB 00:00:00
extras | 3.4 kB 00:00:00
updates | 3.4 kB 00:00:00
(1/2): extras/7/x86_64/primary_db | 147 kB 00:00:00
(2/2): updates/7/x86_64/primary_db | 2.0 MB 00:00:00
Loading mirror speeds from cached hostfile
* base: mirrors.huaweicloud.com
* extras: mirrors.163.com
* updates: mirrors.huaweicloud.com
Resolving Dependencies
--> Running transaction check
---> Package tree.x86_64 0:1.6.0-10.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
===========================================================================================================================
Package Arch Version Repository Size
===========================================================================================================================
Installing:
tree x86_64 1.6.0-10.el7 base 46 k
Transaction Summary
===========================================================================================================================
Install 1 Package
Total download size: 46 k
Installed size: 87 k
Downloading packages:
tree-1.6.0-10.el7.x86_64.rpm | 46 kB 00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : tree-1.6.0-10.el7.x86_64 1/1
Verifying : tree-1.6.0-10.el7.x86_64 1/1
Installed:
tree.x86_64 0:1.6.0-10.el7
Complete!
tree可以简单的可以显示一个文档
tree /
但是由于文件过于多，可能突破Xshell的ScrollBack上限。我们用参数来显示两层目录。查看tree的用法有两种，一种是用tree本身来看，另一种是用Manual Page命令。
[root@lhy ~]# tree --help
usage: tree [-acdfghilnpqrstuvxACDFQNSUX] [-H baseHREF] [-T title ] [-L level [-R]]
[-P pattern] [-I pattern] [-o filename] [--version] [--help] [--inodes]
[--device] [--noreport] [--nolinks] [--dirsfirst] [--charset charset]
[--filelimit[=]#] [--si] [--timefmt[=]<f>] [<directory list>]
------- Listing options -------
-a All files are listed.
-d List directories only.
-l Follow symbolic links like directories.
-f Print the full path prefix for each file.
-x Stay on current filesystem only.
-L level Descend only level directories deep.
-R Rerun tree when max dir level reached.
-P pattern List only those files that match the pattern given.
-I pattern Do not list files that match the given pattern.
--noreport Turn off file/directory count at end of tree listing.
--charset X Use charset X for terminal/HTML and indentation line output.
--filelimit # Do not descend dirs with more than # files in them.
--timefmt <f> Print and format time according to the format <f>.
-o filename Output to file instead of stdout.
--du Print directory sizes.
--prune Prune empty directories from the output.
-------- File options ---------
-q Print non-printable characters as '?'.
-N Print non-printable characters as is.
-Q Quote filenames with double quotes.
-p Print the protections for each file.
-u Displays file owner or UID number.
-g Displays file group owner or GID number.
-s Print the size in bytes of each file.
-h Print the size in a more human readable way.
--si Like -h, but use in SI units (powers of 1000).
-D Print the date of last modification or (-c) status change.
-F Appends '/', '=', '*', '@', '|' or '>' as per ls -F.
--inodes Print inode number of each file.
--device Print device ID number to which each file belongs.
------- Sorting options -------
-v Sort files alphanumerically by version.
-r Sort files in reverse alphanumeric order.
-t Sort files by last modification time.
-c Sort files by last status change time.
-U Leave files unsorted.
--dirsfirst List directories before files (-U disables).
------- Graphics options ------
-i Don't print indentation lines.
-A Print ANSI lines graphic indentation lines.
-S Print with ASCII graphics indentation lines.
-n Turn colorization off always (-C overrides).
-C Turn colorization on always.
------- XML/HTML options -------
-X Prints out an XML representation of the tree.
-H baseHREF Prints out HTML format with baseHREF as top directory.
-T string Replace the default HTML title and H1 header with string.
--nolinks Turn off hyperlinks in HTML output.
---- Miscellaneous options ----
--version Print version and exit.
--help Print usage and this help message and exit.
[root@lhy ~]# man tree
TREE(1) General Commands Manual TREE(1)
NAME
tree - list contents of directories in a tree-like format.
SYNOPSIS
tree [-acdfghilnpqrstuvxACDFQNSUX] [-L level [-R]] [-H baseHREF] [-T title] [-o filename] [--nolinks] [-P pat‐
tern] [-I pattern] [--inodes] [--device] [--noreport] [--dirsfirst] [--version] [--help] [--filelimit #] [--si]
[--prune] [--du] [--timefmt format] [directory ...]
DESCRIPTION
Tree is a recursive directory listing program that produces a depth indented listing of files, which is col‐
orized ala dircolors if the LS_COLORS environment variable is set and output is to tty. With no arguments, tree
lists the files in the current directory. When directory arguments are given, tree lists all the files and/or
directories found in the given directories each in turn. Upon completion of listing all files/directories
found, tree returns the total number of files and/or directories listed.
By default, when a symbolic link is encountered, the path that the symbolic link refers to is printed after the
name of the link in the format:
name -> real-path
If the `-l' option is given and the symbolic link refers to an actual directory, then tree will follow the path
of the symbolic link as if it were a real directory.
OPTIONS
Tree understands the following command line switches:
LISTING OPTIONS
-a All files are printed. By default tree does not print hidden files (those beginning with a dot `.'). In
no event does tree print the file system constructs `.' (current directory) and `..' (previous direc‐
tory).
-d List directories only.
-l Follows symbolic links if they point to directories, as if they were directories. Symbolic links that
will result in recursion are avoided when detected.
-f Prints the full path prefix for each file.
-x Stay on the current file-system only. Ala find -xdev.
-L level
Max display depth of the directory tree.
-R Recursively cross down the tree each level directories (see -L option), and at each of them execute tree
again adding `-o 00Tree.html' as a new option.
-P pattern
List only those files that match the wild-card pattern. Note: you must use the -a option to also con‐
sider those files beginning with a dot `.' for matching. Valid wildcard operators are `*' (any zero or
more characters), `?' (any single character), `[...]' (any single character listed between brackets
(optional - (dash) for character range may be used: ex: [A-Z]), and `[^...]' (any single character not
listed in brackets) and `|' separates alternate patterns.
-I pattern
Do not list those files that match the wild-card pattern.
--prune
Makes tree prune empty directories from the output, useful when used in conjunction with -P or -I. See
BUGS AND NOTES below for more information on this option.
--noreport
Omits printing of the file and directory report at the end of the tree listing.
--charset charset
Set the character set to use when outputting HTML and for line drawing.
--filelimit #
Do not descend directories that contain more than # entries.
--timefmt format
Prints (implies -D) and formats the date according to the format string which uses the strftime(3) syn‐
tax.
-o filename
Send output to filename.
FILE OPTIONS
-q Print non-printable characters in filenames as question marks instead of the default.
-N Print non-printable characters as is instead of as escaped octal numbers.
-Q Quote the names of files in double quotes.
-p Print the file type and permissions for each file (as per ls -l).
-u Print the username, or UID # if no username is available, of the file.
-g Print the group name, or GID # if no group name is available, of the file.
-s Print the size of each file in bytes along with the name.
-h Print the size of each file but in a more human readable way, e.g. appending a size letter for kilobytes
(K), megabytes (M), gigabytes (G), terabytes (T), petabytes (P) and exabytes (E).
--si Like -h but use SI units (powers of 1000) instead.
--du For each directory report its size as the accumulation of sizes of all its files and sub-directories (and
their files, and so on). The total amount of used space is also given in the final report (like the 'du
-c' command.) This option requires tree to read the entire directory tree before emitting it, see BUGS
AND NOTES below. Implies -s.
-D Print the date of the last modification time or if -c is used, the last status change time for the file
listed.
-F Append a `/' for directories, a `=' for socket files, a `*' for executable files, a `>' for doors
(Solaris) and a `|' for FIFO's, as per ls -F
-F Append a `/' for directories, a `=' for socket files, a `*' for executable files, a `>' for doors
(Solaris) and a `|' for FIFO's, as per ls -F
--inodes
Prints the inode number of the file or directory
--device
Prints the device number to which the file or directory belongs
SORTING OPTIONS
-v Sort the output by version.
-r Sort the output in reverse alphabetic order.
-t Sort the output by last modification time instead of alphabetically.
-c Sort the output by last status change instead of alphabetically. Modifies the -D option (if used) to
print the last status change instead of modification time.
-U Do not sort. Lists files in directory order. Disables --dirsfirst.
--dirsfirst
List directories before files. This is a meta-sort that alters the above sorts. This option is disabled
when -U is used.
GRAPHICS OPTIONS
-i Makes tree not print the indentation lines, useful when used in conjunction with the -f option.
-A Turn on ANSI line graphics hack when printing the indentation lines.
-S Turn on ASCII line graphics (useful when using Linux console mode fonts). This option is now equivalent
to `--charset=IBM437' and may eventually be depreciated.
-n Turn colorization off always, over-ridden by the -C option.
-C Turn colorization on always, using built-in color defaults if the LS_COLORS environment variable is not
set. Useful to colorize output to a pipe.
XML/HTML OPTIONS
-X Turn on XML output. Outputs the directory tree as an XML formatted file.
-H baseHREF
Turn on HTML output, including HTTP references. Useful for ftp sites. baseHREF gives the base ftp loca‐
tion when using HTML output. That is, the local directory may be `/local/ftp/pub', but it must be refer‐
enced as `ftp://hostname.organization.domain/pub' (baseHREF should be `ftp://hostname.organiza‐
tion.domain'). Hint: don't use ANSI lines with this option, and don't give more than one directory in the
directory list. If you wish to use colors via CCS style-sheet, use the -C option in addition to this
option to force color output.
-T title
Sets the title and H1 header string in HTML output mode.
--nolinks
Turns off hyperlinks in HTML output.
MISC OPTIONS
--help Outputs a verbose usage listing.
--version
Outputs the version of tree.
FILES
/etc/DIR_COLORS System color database.
~/.dircolors Users color database.
ENVIRONMENT
LS_COLORS Color information created by dircolors
TREE_COLORS Uses this for color information over LS_COLORS if it is set.
TREE_CHARSET Character set for tree to use in HTML mode.
LC_CTYPE Locale for filename output.
LC_TIME Locale for timefmt output, see strftime(3).
TZ Timezone for timefmt output, see strftime(3).
AUTHOR
Steve Baker (ice@mama.indstate.edu)
HTML output hacked by Francesc Rocher (rocher@econ.udg.es)
Charsets and OS/2 support by Kyosuke Tokoro (NBG01720@nifty.ne.jp)
BUGS AND NOTES
Tree does not prune "empty" directories when the -P and -I options are used by default. Use the --prune option.
The -h and --si options round to the nearest whole number unlike the ls implementations which rounds up always.
Pruning files and directories with the -I, -P and --filelimit options will lead to incorrect file/directory
count reports.
The --prune and --du options cause tree to accumulate the entire tree in memory before emitting it. For large
directory trees this can cause a significant delay in output and the use of large amounts of memory.
The timefmt expansion buffer is limited to a ridiculously large 255 characters. Output of time strings longer
than this will be undefined, but are guaranteed to not exceed 255 characters.
XML trees are not colored, which is a bit of a shame.
Probably more.
SEE ALSO
dircolors(1), ls(1), find(1), du(1), strftime(3)
Tree 1.6.0
Manual page tree(1) line 1 (press h for help or q to quit)
可以看到用-L参数可以设置最深搜索层数，-d只显示文件夹。
[root@lhy ~]# tree / -L 2 -d
/
├── bin -> usr/bin
├── boot
│ ├── efi
│ ├── grub
│ └── grub2
├── dev
│ ├── block
│ ├── bsg
│ ├── bus
│ ├── char
│ ├── cpu
│ ├── disk
│ ├── dri
│ ├── fd -> /proc/self/fd
│ ├── hugepages
│ ├── input
│ ├── mapper
│ ├── mqueue
│ ├── net
│ ├── pts
│ ├── raw
│ ├── shm
│ ├── snd
│ └── vfio
├── etc
│ ├── alternatives
│ ├── audisp
│ ├── audit
│ ├── bash_completion.d
│ ├── binfmt.d
│ ├── chkconfig.d
│ ├── cron.d
│ ├── cron.daily
│ ├── cron.hourly
│ ├── cron.monthly
│ ├── cron.weekly
│ ├── dbus-1
│ ├── default
│ ├── depmod.d
│ ├── dhcp
│ ├── dracut.conf.d
│ ├── firewalld
│ ├── gcrypt
│ ├── gnupg
│ ├── groff
│ ├── grub.d
│ ├── gss
│ ├── init.d -> rc.d/init.d
│ ├── iproute2
│ ├── kernel
│ ├── krb5.conf.d
│ ├── ld.so.conf.d
│ ├── libnl
│ ├── logrotate.d
│ ├── modprobe.d
│ ├── modules-load.d
│ ├── my.cnf.d
│ ├── NetworkManager
│ ├── openldap
│ ├── opt
│ ├── pam.d
│ ├── pkcs11
│ ├── pki
│ ├── plymouth
│ ├── pm
│ ├── polkit-1
│ ├── popt.d
│ ├── postfix
│ ├── ppp
│ ├── prelink.conf.d
│ ├── profile.d
│ ├── python
│ ├── rc0.d -> rc.d/rc0.d
│ ├── rc1.d -> rc.d/rc1.d
│ ├── rc2.d -> rc.d/rc2.d
│ ├── rc3.d -> rc.d/rc3.d
│ ├── rc4.d -> rc.d/rc4.d
│ ├── rc5.d -> rc.d/rc5.d
│ ├── rc6.d -> rc.d/rc6.d
│ ├── rc.d
│ ├── rpm
│ ├── rsyslog.d
│ ├── rwtab.d
│ ├── sasl2
│ ├── security
│ ├── selinux
│ ├── sgml
│ ├── skel
│ ├── ssh
│ ├── ssl
│ ├── statetab.d
│ ├── sudoers.d
│ ├── sysconfig
│ ├── sysctl.d
│ ├── systemd
│ ├── terminfo
│ ├── tmpfiles.d
│ ├── tuned
│ ├── udev
│ ├── vmware-tools
│ ├── wpa_supplicant
│ ├── X11
│ ├── xdg
│ ├── xinetd.d
│ ├── xml
│ ├── yum
│ └── yum.repos.d
├── home
│ └── lhy01
├── lib -> usr/lib
├── lib64 -> usr/lib64
├── media
├── mnt
├── opt
├── proc
│ ├── 1
│ ├── 10
│ ├── 11
│ ├── acpi
│ ├── asound
│ ├── bus
│ ├── driver
│ ├── fs
│ ├── irq
│ ├── mpt
│ ├── net -> self/net
│ ├── scsi
│ ├── self -> 1879
│ ├── sys
│ ├── sysvipc
│ └── tty
├── root
│ └── openscap_data
├── run
│ ├── console
│ ├── dbus
│ ├── faillock
│ ├── firewalld
│ ├── initramfs
│ ├── lock
│ ├── log
│ ├── mount
│ ├── netreport
│ ├── NetworkManager
│ ├── plymouth
│ ├── sepermit
│ ├── setrans
│ ├── sudo
│ ├── systemd
│ ├── tmpfiles.d
│ ├── tuned
│ ├── udev
│ ├── user
│ └── vmware
├── sbin -> usr/sbin
├── srv
├── sys
│ ├── block
│ ├── bus
│ ├── class
│ ├── dev
│ ├── devices
│ ├── firmware
│ ├── fs
│ ├── hypervisor
│ ├── kernel
│ ├── module
│ └── power
├── tmp
│ ├── systemd-private-72a51b409754493b803ada2e9f1e8ca6-vgauthd.service-SJRZXu
│ ├── systemd-private-72a51b409754493b803ada2e9f1e8ca6-vmtoolsd.service-Ct0xiS
│ ├── systemd-private-b5d827de47c64188ae996c7b05c8f1b2-vgauthd.service-SHMZTz
│ └── systemd-private-b5d827de47c64188ae996c7b05c8f1b2-vmtoolsd.service-LXMW2A
├── usr
│ ├── bin
│ ├── etc
│ ├── games
│ ├── include
│ ├── lib
│ ├── lib64
│ ├── libexec
│ ├── local
│ ├── sbin
│ ├── share
│ ├── src
│ └── tmp -> ../var/tmp
└── var
├── adm
├── cache
├── crash
├── db
├── empty
├── games
├── gopher
├── kerberos
├── lib
├── local
├── lock -> ../run/lock
├── log
├── mail -> spool/mail
├── nis
├── opt
├── preserve
├── run -> ../run
├── spool
├── tmp
└── yp
370 directories
目录/usr/bin/ /usr/sbin/ /bin/ /sbin/ 这几个目录中保存的是一系列的命令。为什么直接敲命令而不需要执行具体目录下的文件，这是因为环境变量PATH的作用，这点之后再讲。
/sbin/下的命令一般是root用户的命令，普通用户下的命令一般是/bin/下的。
[root@lhy ~]# ls /sbin/
accessdb e2fsck ip nl-link-list sestatus
addgnupghome e2image ip6tables nl-pktloc-lookup setcap
addpart e2label ip6tables-restore nl-qdisc-add setenforce
adduser e2undo ip6tables-save nl-qdisc-delete setfiles
agetty e4defrag ipmaddr nl-qdisc-list setpci
aide eapol_test iprconfig nologin setsebool
alternatives ebtables iprdbg nstat sfdisk
anacron ebtables-restore iprdump ownership shutdown
applygnupgdefaults ebtables-save iprinit packer slattach
arp ether-wake iprsos pam_console_apply sln
arpd ethtool iprupdate pam_tally2 smtp-sink
arping faillock ipset pam_timestamp_check smtp-source
audispd fdformat iptables parted ss
auditctl fdisk iptables-restore partprobe sshd
auditd filefrag iptables-save partx sshd-keygen
augenrules findfs iptunnel pidof sulogin
aureport firewalld irqbalance ping6 sushell
ausearch fixfiles kdump pivot_root swaplabel
authconfig fsck kexec plipconfig swapoff
authconfig-tui fsck.btrfs killall5 plymouthd swapon
autrace fsck.cramfs kpartx plymouth-set-default-theme switch_root
avcstat fsck.ext2 lchage postalias sysctl
badblocks fsck.ext3 ldattach postcat sys-unconfig
biosdecode fsck.ext4 ldconfig postconf tc
biosdevname fsck.minix lgroupadd postdrop telinit
blkdeactivate fsck.xfs lgroupdel postfix tracepath
blkdiscard fsfreeze lgroupmod postkick tracepath6
blkid fstrim lid postlock tune2fs
blockdev fxload lnewusers postlog tuned
bridge genhomedircon lnstat postmap tuned-adm
btrfs genhostid load_policy postmulti udevadm
btrfsck genl logrotate postqueue unix_chkpwd
btrfs-convert genl-ctrl-list logsave postsuper unix_update
btrfs-debug-tree getcap losetup poweroff update-alternatives
btrfs-find-root getenforce lpasswd ppp-watch update-pciids
btrfs-image getpcaps lsmod pwck useradd
btrfs-map-logical getsebool lspci pwconv userdel
btrfs-select-super glibc_post_upgrade.x86_64 luseradd pwhistory_helper usermod
btrfstune groupadd luserdel pwunconv usernetctl
btrfs-zero-log groupdel lusermod rdisc vigr
build-locale-archive groupmems makedumpfile readprofile vipw
cacertdir_rehash groupmod matchpathcon reboot virt-what
capsh grpck mii-diag resize2fs visudo
cbq grpconv mii-tool resizepart vmcore-dmesg
cfdisk grpunconv mkdict restorecon vpddecode
chcpu grub2-bios-setup mkdumprd rmmod weak-modules
chkconfig grub2-get-kernel-settings mke2fs route wipefs
chpasswd grub2-install mkfs routef wpa_cli
chroot grub2-mkconfig mkfs.btrfs routel wpa_passphrase
clock grub2-ofpathname mkfs.cramfs rsyslogd wpa_supplicant
clockdiff grub2-probe mkfs.ext2 rtacct xfs_admin
consoletype grub2-reboot mkfs.ext3 rtcwake xfs_bmap
cracklib-check grub2-rpm-sort mkfs.ext4 rtmon xfs_copy
cracklib-format grub2-set-default mkfs.minix rtpr xfs_db
cracklib-packer grub2-setpassword mkfs.xfs rtstat xfs_estimate
cracklib-unpacker grub2-sparc64-setup mkhomedir_helper runlevel xfs_freeze
create-cracklib-dict grubby mklost+found runuser xfs_fsr
crond halt mkswap sasldblistusers2 xfs_growfs
ctrlaltdel hardlink modinfo saslpasswd2 xfs_info
ctstat hwclock modprobe sefcontext_compile xfs_io
debugfs iconvconfig mount.fuse selabel_digest xfs_logprint
delpart iconvconfig.x86_64 nameif selabel_lookup xfs_mdrestore
depmod ifcfg netreport selabel_lookup_best_match xfs_metadump
devlink ifconfig NetworkManager selabel_partial_match xfs_mkfile
dhclient ifdown new-kernel-pkg selinuxconlist xfs_ncheck
dhclient-script ifenslave newusers selinuxdefcon xfs_quota
dmfilemapd ifstat nl-class-add selinuxenabled xfs_repair
dmidecode ifup nl-class-delete selinuxexeccon xfs_rtcp
dmsetup init nl-classid-lookup selinux_restorecon xtables-multi
dmstats insmod nl-class-list semodule zdump
dracut install-info nl-cls-add sendmail zic
dumpe2fs installkernel nl-cls-delete sendmail.postfix zramctl
e2freefrag intel-microcode2ucode nl-cls-list service
[root@lhy ~]# ls /bin/
[ groups nl-link-set sotruss
a2p grub2-editenv nl-link-stats splain
addr2line grub2-file nl-list-caches split
alias grub2-fstest nl-list-sockets sprof
apropos grub2-glue-efi nl-monitor sqlite3
ar grub2-kbdcomp nl-neigh-add ssh
arch grub2-menulst2cfg nl-neigh-delete ssh-add
as grub2-mkfont nl-neigh-list ssh-agent
aserver grub2-mkimage nl-neightbl-list ssh-copy-id
aulast grub2-mklayout nl-pktloc-lookup ssh-keygen
aulastlog grub2-mknetdir nl-qdisc-add ssh-keyscan
ausyscall grub2-mkpasswd-pbkdf2 nl-qdisc-delete ssltap
auvirt grub2-mkrelpath nl-qdisc-list stat
awk grub2-mkrescue nl-route-add stdbuf
base64 grub2-mkstandalone nl-route-delete strings
basename grub2-script-check nl-route-get strip
bash grub2-syslinux2cfg nl-route-list stty
bashbug gsettings nl-rule-list su
bashbug-64 gsoelim nl-tctree-list sudo
bg gtar nl-util-addr sudoedit
bond2team gtbl nm sudoreplay
bootctl gtroff nmcli sum
busctl gunzip nm-online sync
c2ph gzexe nmtui systemctl
cal gzip nmtui-connect systemd-analyze
ca-legacy h2ph nmtui-edit systemd-ask-password
captoinfo hdsploader nmtui-hostname systemd-cat
cat head nohup systemd-cgls
catchsegv hexdump nproc systemd-cgtop
catman hostid nroff systemd-coredumpctl
cd hostname nsenter systemd-delta
centrino-decode hostnamectl numfmt systemd-detect-virt
certutil i386 objcopy systemd-escape
c++filt iconv objdump systemd-firstboot
chacl id od systemd-hwdb
chage idiag-socket-details oldfind systemd-inhibit
chattr idn open systemd-loginctl
chcon igawk openssl systemd-machine-id-setup
chfn info openvt systemd-notify
chgrp infocmp oscap systemd-nspawn
chmod infokey os-prober systemd-path
chown infotocap p11-kit systemd-run
chrt install passwd systemd-stdio-bridge
chsh ionice paste systemd-sysv-convert
chvt ipcalc pathchk systemd-tmpfiles
cksum ipcmk pchrt systemd-tty-ask-password-agent
clear ipcrm perl tabs
cmp ipcs perl5.16.3 tac
cmsutil iptables-xml perlbug tail
col isosize perldoc tailf
colcrt jobs perlthanks tar
colrm join pflags taskset
column journalctl pgawk tbl
comm kbdinfo pgrep teamd
command kbd_mode pic teamdctl
coredumpctl kbdrate piconv teamnl
cp kdumpctl pinentry tee
cpio kernel-install pinentry-curses test
cpupower kill ping testgdbm
crlutil kmod ping6 tic
crontab last pinky timedatectl
csplit lastb pk12util timeout
csslint-0.6 lastlog pkaction tload
curl lchfn pkcheck tmon
cut lchsh pkexec toe
date ld pkg-config top
db_archive ld.bfd pkill touch
db_checkpoint ldd pkla-admin-identities tput
db_deadlock ld.gold pkla-check-authorization tr
db_dump less pkttyagent tracepath
db_dump185 lessecho pl2pm tracepath6
db_hotbackup lesskey pldd tree
db_load lesspipe.sh plymouth troff
db_log_verify lexgrog pmap true
db_printlog link pod2html truncate
db_recover linux32 pod2man trust
db_replicate linux64 pod2text tset
db_stat linux-boot-prober pod2usage tsort
db_tuner ln post-grohtml tty
db_upgrade loadkeys powernow-k8-decode turbostat
dbus-binding-tool loadunimap pr tzselect
dbus-cleanup-sockets locale preconv udevadm
dbus-daemon localectl pre-grohtml ul
dbus-monitor localedef printenv ulockmgr_server
dbus-send logger printf umask
dbus-uuidgen login prlimit umount
db_verify loginctl ps unalias
dd logname psed uname
deallocvt look psfaddtable unexpand
df ls psfgettable unicode_start
dgawk lsattr psfstriptable unicode_stop
diff lsblk psfxtable uniq
diff3 lscpu pstruct unlink
dir lsinitrd ptaskset unshare
dircolors lsipc ptx unxz
dirname lslocks pwd update-ca-trust
dmesg lslogins pwdx update-mime-database
dnsdomainname lsns pwmake uptime
domainname lsscsi pwscore urlgrabber
dracut lua pydoc users
du luac python usleep
dumpkeys machinectl python2 usx2yloader
dwp mailq python2.7 utmpdump
echo mailq.postfix ranlib uuidgen
egrep make raw vdir
eject makedb read VGAuthService
elfedit man readelf vi
env mandb readlink view
envsubst manpath realpath vim
eqn mapscrn recode-sr-latin vimdiff
ex mcookie rename vimtutor
expand md5sum renice vlock
expr mesg reset vmhgfs-fuse
factor mixartloader resizecons vmstat
fallocate mkdir rev vm-support
false mkfifo rm vmtoolsd
fc mkinitrd rmail vmware-checkvm
fg mknod rmail.postfix vmware-guestproxycerttool
fgconsole mktemp rmdir vmware-hgfsclient
fgrep modutil rpcgen vmware-namespace-cmd
file more rpm vmware-rpctool
find mount rpm2cpio vmware-toolbox-cmd
find2perl mountpoint rpmdb vmware-vgauth-cmd
findmnt msgattrib rpmkeys vmware-xferlogs
fipscheck msgcat rpmquery vxloader
fipshmac msgcmp rpmverify w
firewall-cmd msgcomm rsyslog-recover-qi.pl wait
firewall-offline-cmd msgconv runcon wall
flock msgen run-parts watch
fmt msgexec rvi watchgnupg
fold msgfilter rview wc
free msgfmt rvim wdctl
fusermount msggrep s2p whatis
gapplication msghack scp whereis
gawk msginit script which
gdbus msgmerge scriptreplay whiptail
gencat msgunfmt sdiff who
genl-ctrl-list msguniq secon whoami
geoiplookup mv sed write
geoiplookup6 namei seq x86_64
geoipupdate ndptool setarch x86_energy_perf_policy
geqn neqn setfacl xargs
getconf netstat setfont xgettext
getent newaliases setkeycodes xmlcatalog
getfacl newaliases.postfix setleds xmllint
getkeycodes newgrp setmetamode xmlsec1
getopt nf-ct-add setpriv xmlwf
getopts nf-ct-list setsid xsltproc
gettext nf-exp-add setterm xxd
gettext.sh nf-exp-delete setup-nsssysinit xz
gio nf-exp-list setup-nsssysinit.sh xzcat
gio-querymodules-64 nf-log setvtrgb xzcmp
glib-compile-schemas nf-monitor sftp xzdec
gmake nf-queue sg xzdiff
gneqn ngettext sh xzegrep
gnroff nice sha1sum xzfgrep
gpasswd nisdomainname sha224sum xzgrep
gpg nl sha256sum xzless
gpg2 nl-addr-add sha384sum xzmore
gpg-agent nl-addr-delete sha512sum yes
gpgconf nl-addr-list showconsolefont ypdomainname
gpg-connect-agent nl-class-add showkey yum
gpg-error nl-class-delete shred zcat
gpgparsemail nl-classid-lookup shuf zcmp
gpgsplit nl-class-list signtool zdiff
gpgv nl-cls-add signver zegrep
gpgv2 nl-cls-delete size zfgrep
gpg-zip nl-cls-list skill zforce
gpic nl-fib-lookup slabtop zgrep
gprof nl-link-enslave sleep zless
grep nl-link-ifindex2name slogin zmore
groff nl-link-list snice znew
grops nl-link-name2ifindex soelim zsoelim
grotty nl-link-release sort
/boot/下的文件是启动相关的文件，比如grub文件。比如删除了vmlinuz-3.10.0-693.el7.x86_64这些文件，你就不能正常启动这个系统了。
[root@lhy ~]# ls /boot/
config-3.10.0-693.el7.x86_64 initramfs-3.10.0-693.el7.x86_64kdump.img
efi initrd-plymouth.img
grub symvers-3.10.0-693.el7.x86_64.gz
grub2 System.map-3.10.0-693.el7.x86_64
initramfs-0-rescue-7b83625f83564e1691eca0a488be153c.img vmlinuz-0-rescue-7b83625f83564e1691eca0a488be153c
initramfs-3.10.0-693.el7.x86_64.img vmlinuz-3.10.0-693.el7.x86_64
/dev/文件是linux系统的特有的设备文件，鼠标、键盘、显示器等文件都保存在这里。
[root@lhy ~]# ls /dev/
agpgart dmmidi log port shm tty14 tty27 tty4 tty52 tty8 vcs vfio
autofs dri loop-control ppp snapshot tty15 tty28 tty40 tty53 tty9 vcs1 vga_arbiter
block fb0 mapper ptmx snd tty16 tty29 tty41 tty54 ttyS0 vcs2 vhci
bsg fd mcelog pts sr0 tty17 tty3 tty42 tty55 ttyS1 vcs3 vhost-net
btrfs-control fd0 mem random stderr tty18 tty30 tty43 tty56 ttyS2 vcs4 vmci
bus full midi raw stdin tty19 tty31 tty44 tty57 ttyS3 vcs5 vsock
cdrom fuse mqueue rtc stdout tty2 tty32 tty45 tty58 uhid vcs6 zero
char hidraw0 net rtc0 tty tty20 tty33 tty46 tty59 uinput vcsa
console hpet network_latency sda tty0 tty21 tty34 tty47 tty6 urandom vcsa1
core hugepages network_throughput sda1 tty1 tty22 tty35 tty48 tty60 usbmon0 vcsa2
cpu hwrng null sda2 tty10 tty23 tty36 tty49 tty61 usbmon1 vcsa3
cpu_dma_latency initctl nvram sda3 tty11 tty24 tty37 tty5 tty62 usbmon2 vcsa4
crash input oldmem sg0 tty12 tty25 tty38 tty50 tty63 usbmon3 vcsa5
disk kmsg parport0 sg1 tty13 tty26 tty39 tty51 tty7 usbmon4 vcsa6
/etc/文件夹是系统的配置文件所在的位置。
[root@lhy ~]# ls /etc/sysconfig/network-scripts/ifcfg-ens33
/etc/sysconfig/network-scripts/ifcfg-ens33
[root@lhy ~]# ls /etc/ssh/sshd_config
/etc/ssh/sshd_config
[root@lhy ~]# ls /etc/
adjtime ethertypes ld.so.conf popt.d skel
aide.conf exports ld.so.conf.d postfix ssh
aliases favicon.png libaudit.conf ppp ssl
aliases.db filesystems libnl prelink.conf.d statetab
alternatives firewalld libuser.conf printcap statetab.d
anacrontab fstab locale.conf profile subgid
asound.conf fuse.conf localtime profile.d subuid
audisp gcrypt login.defs protocols sudo.conf
audit GeoIP.conf logrotate.conf python sudoers
bash_completion.d GeoIP.conf.default logrotate.d rc0.d sudoers.d
bashrc gnupg machine-id rc1.d sudo-ldap.conf
binfmt.d GREP_COLORS magic rc2.d sysconfig
centos-release groff makedumpfile.conf.sample rc3.d sysctl.conf
centos-release-upstream group man_db.conf rc4.d sysctl.d
chkconfig.d group- mke2fs.conf rc5.d systemd
cron.d grub2.cfg modprobe.d rc6.d system-release
cron.daily grub.d modules-load.d rc.d system-release-cpe
cron.deny gshadow motd rc.local terminfo
cron.hourly gshadow- mtab redhat-release tmpfiles.d
cron.monthly gss my.cnf resolv.conf tuned
crontab host.conf my.cnf.d rpc udev
cron.weekly hostname NetworkManager rpm vconsole.conf
crypttab hosts networks rsyslog.conf vimrc
csh.cshrc hosts.allow nsswitch.conf rsyslog.d virc
csh.login hosts.deny nsswitch.conf.bak rwtab vmware-tools
dbus-1 init.d openldap rwtab.d wpa_supplicant
default inittab opt sasl2 X11
depmod.d inputrc os-release securetty xdg
dhcp iproute2 pam.d security xinetd.d
DIR_COLORS issue passwd selinux xml
DIR_COLORS.256color issue.net passwd- services yum
DIR_COLORS.lightbgcolor kdump.conf pkcs11 sestatus.conf yum.conf
dracut.conf kernel pki sgml yum.repos.d
dracut.conf.d krb5.conf plymouth shadow
e2fsck.conf krb5.conf.d pm shadow-
environment ld.so.cache polkit-1 shells
/home/是用户的家目录，存用户的文件，类比于/root/
[root@lhy ~]# ls /home/
lhy01
/lib/ /lib64/等文件夹存的是库文件。库文件类似于Windows下的×.dll文件。可以用ldd命令查看某个命令的依赖库。
[root@lhy ~]# ldd /bin/ls
linux-vdso.so.1 => (0x00007ffd4e88f000)
libselinux.so.1 => /lib64/libselinux.so.1 (0x00007feffcfcf000)
libcap.so.2 => /lib64/libcap.so.2 (0x00007feffcdca000)
libacl.so.1 => /lib64/libacl.so.1 (0x00007feffcbc0000)
libc.so.6 => /lib64/libc.so.6 (0x00007feffc7fd000)
libpcre.so.1 => /lib64/libpcre.so.1 (0x00007feffc59b000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007feffc396000)
/lib64/ld-linux-x86-64.so.2 (0x00005636e812b000)
libattr.so.1 => /lib64/libattr.so.1 (0x00007feffc191000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007feffbf75000)
CentOS7之后，CentOS操作系统就没有32位系统了。32位和64位系统的最大的区别就在于识别的内存大小不一样。如果是32位的系统，只能识别4GB内存，由于操作系统本身内存占用以及地址保留，实际可以使用的内存空间为3.2G左右。
/media/目录是媒介目录，默认是空的。如果插入优盘、硬盘，系统会自动挂载到/media目录。
/mnt/是挂载目录 ，默认也为空，可以把想要的文件系统挂载到此处。
/opt/默认也是空目录，是按完系统后你又需要安装其他的应用软件，一般是源码包的软件，可以自己指定路径，管理员习惯性的把软件按在这，你也可以安装在其他位置。
/proc/存放的是进程文件，每一个进程都有一个目录，文件夹名为PID
[root@lhy ~]# ls /proc/
1 16 265 291 304 319 332 346 399 55 641 acpi filesystems mdstat softirqs
10 17 267 292 305 32 333 347 40 56 642 asound fs meminfo stat
11 18 268 293 306 320 334 3535 400 57 644 buddyinfo interrupts misc swaps
111 1805 27 294 307 321 335 372 401 580 645 bus iomem modules sys
12 2 272 295 308 322 336 373 4018 581 647 cgroups ioports mounts sysrq-trigger
1202 20 273 296 309 323 337 380 41 582 653 cmdline irq mpt sysvipc
1203 21 274 297 31 324 338 383 42 583 666 consoles kallsyms mtrr timer_list
1204 22 2763 298 311 325 339 391 4259 584 679 cpuinfo kcore net timer_stats
1269 23 28 299 312 326 34 392 43 585 7 crypto keys pagetypeinfo tty
1288 24 285 3 313 327 340 393 468 586 76 devices key-users partitions uptime
1293 25 287 30 314 328 341 394 470 587 77 diskstats kmsg sched_debug version
13 258 288 300 315 329 342 395 491 610 8 dma kpagecount schedstat vmallocinfo
1346 260 289 301 316 33 343 396 5 634 9 driver kpageflags scsi vmstat
15 263 29 302 317 330 344 397 51 636 969 execdomains loadavg self zoneinfo
1525 264 290 303 318 331 345 398 53 637 970 fb locks slabinfo
查看某一个PID进程的文件，比如/proc/285/。其中有一个cwd，这个是进程所在的路径。比如我对于某个进程不熟悉，我就根据PID来查看这个进程是从哪执行，执行什么命令（comm文件）。
[root@lhy ~]# ls -l /proc/285/
ls: cannot read symbolic link /proc/285/exe: No such file or directory
total 0
dr-xr-xr-x. 2 root root 0 Jun 2 23:57 attr
-rw-r--r--. 1 root root 0 Jun 2 23:57 autogroup
-r--------. 1 root root 0 Jun 2 23:57 auxv
-r--r--r--. 1 root root 0 Jun 2 23:57 cgroup
--w-------. 1 root root 0 Jun 2 23:57 clear_refs
-r--r--r--. 1 root root 0 Jun 2 23:36 cmdline
-rw-r--r--. 1 root root 0 Jun 2 23:57 comm
-rw-r--r--. 1 root root 0 Jun 2 23:57 coredump_filter
-r--r--r--. 1 root root 0 Jun 2 23:57 cpuset
lrwxrwxrwx. 1 root root 0 Jun 2 23:57 cwd -> /
-r--------. 1 root root 0 Jun 2 23:57 environ
lrwxrwxrwx. 1 root root 0 Jun 2 23:57 exe
dr-x------. 2 root root 0 Jun 2 23:57 fd
dr-x------. 2 root root 0 Jun 2 23:57 fdinfo
-rw-r--r--. 1 root root 0 Jun 2 23:57 gid_map
-r--------. 1 root root 0 Jun 2 23:57 io
-r--r--r--. 1 root root 0 Jun 2 23:57 limits
-rw-r--r--. 1 root root 0 Jun 2 23:57 loginuid
dr-x------. 2 root root 0 Jun 2 23:57 map_files
-r--r--r--. 1 root root 0 Jun 2 23:57 maps
-rw-------. 1 root root 0 Jun 2 23:57 mem
-r--r--r--. 1 root root 0 Jun 2 23:57 mountinfo
-r--r--r--. 1 root root 0 Jun 2 23:57 mounts
-r--------. 1 root root 0 Jun 2 23:57 mountstats
dr-xr-xr-x. 5 root root 0 Jun 2 23:57 net
dr-x--x--x. 2 root root 0 Jun 2 23:57 ns
-r--r--r--. 1 root root 0 Jun 2 23:57 numa_maps
-rw-r--r--. 1 root root 0 Jun 2 23:57 oom_adj
-r--r--r--. 1 root root 0 Jun 2 23:57 oom_score
-rw-r--r--. 1 root root 0 Jun 2 23:57 oom_score_adj
-r--r--r--. 1 root root 0 Jun 2 23:57 pagemap
-r--r--r--. 1 root root 0 Jun 2 23:57 personality
-rw-r--r--. 1 root root 0 Jun 2 23:57 projid_map
lrwxrwxrwx. 1 root root 0 Jun 2 23:57 root -> /
-rw-r--r--. 1 root root 0 Jun 2 23:57 sched
-r--r--r--. 1 root root 0 Jun 2 23:57 schedstat
-r--r--r--. 1 root root 0 Jun 2 23:57 sessionid
-rw-r--r--. 1 root root 0 Jun 2 23:57 setgroups
-r--r--r--. 1 root root 0 Jun 2 23:57 smaps
-r--r--r--. 1 root root 0 Jun 2 23:57 stack
-r--r--r--. 1 root root 0 Jun 2 23:57 stat
-r--r--r--. 1 root root 0 Jun 2 23:57 statm
-r--r--r--. 1 root root 0 Jun 2 23:36 status
-r--r--r--. 1 root root 0 Jun 2 23:57 syscall
dr-xr-xr-x. 3 root root 0 Jun 2 23:57 task
-r--r--r--. 1 root root 0 Jun 2 23:57 timers
-rw-r--r--. 1 root root 0 Jun 2 23:57 uid_map
-r--r--r--. 1 root root 0 Jun 2 23:57 wchan
/run/是进程产生的临时文件，关机就会消失。
[root@lhy ~]# ls /run/
auditd.pid cron.reboot firewalld log NetworkManager setrans syslogd.pid tuned utmp
console dbus initramfs mount plymouth sshd.pid systemd udev vmware
crond.pid faillock lock netreport sepermit sudo tmpfiles.d user xtables.lock
/srv/文件夹默认是空的，存系统服务产生的一些文件。
/sys/存系统内核相关的文件，一般我们不去修改它们。
/tmp/是临时文件夹，任何用户都可以向其中添加文件，权限宽泛，但是普通用户之间的文件自己管理，有特殊权限，之后会讲。
/usr/是系统用户的目录，类似于根目录。
/var/目录存储的日志文件。比如系统日志存在/var/log/messages里面。
2.3 ls命令
ls命令可以列出当前目录的文件和文件夹，这是一个非常常用的一个命令，下面会介绍一下其常用参数。
列出文件的详细信息，使用参数-l
[root@lhy ~]# ls -l
total 4
-rw-------. 1 root root 1622 May 29 14:05 anaconda-ks.cfg
drwxr-xr-x. 2 root root 40 May 29 14:04 openscap_data
第一列是文件类型与权限，第二列表示有多少文件使用了相同的inode，inode记录的是这个文件的存储位置。inode指向的是固定的一个存储块，如果两个文件inode号相同，那么它们存储的位置就是相同的，这个和后续的硬链接有关，暂且不表。第三列表示所有者，第四列表示所属组。第五列是文件大小，单位是Byte。后面就是创建时间和文件名。
查看某一文件的inode使用-i参数。
[root@lhy ~]# ls -i anaconda-ks.cfg
67145602 anaconda-ks.cfg
使用-h可以更人性化的查看文件大小。
[root@lhy ~]# ls -lh
total 4.0K
-rw-------. 1 root root 1.6K May 29 14:05 anaconda-ks.cfg
drwxr-xr-x. 2 root root 40 May 29 14:04 openscap_data
使用-a可以查看所有文件，包括隐藏文件、隐藏目录。
[root@lhy ~]# ls -la
total 36
dr-xr-x---. 4 root root 184 Jun 1 11:53 .
dr-xr-xr-x. 17 root root 245 May 31 15:43 ..
-rw-------. 1 root root 1622 May 29 14:05 anaconda-ks.cfg
-rw-------. 1 root root 3206 Jun 1 13:52 .bash_history
-rw-r--r--. 1 root root 18 Dec 29 2013 .bash_logout
-rw-r--r--. 1 root root 176 Dec 29 2013 .bash_profile
-rw-r--r--. 1 root root 176 Dec 29 2013 .bashrc
-rw-r--r--. 1 root root 100 Dec 29 2013 .cshrc
drwxr-xr-x. 2 root root 40 May 29 14:04 openscap_data
drwx------. 2 root root 80 May 31 16:47 .ssh
-rw-r--r--. 1 root root 129 Dec 29 2013 .tcshrc
-rw-------. 1 root root 6877 Jun 1 11:53 .viminfo
每个目录下面都会有两个目录叫做当前目录（./）上一级目录（../），下面显示的就是为什么/root/的inode是4，因为有四个相同的目录指向同一个位置。一般来说对于目录来说，这个inode的个数和其下子目录数相同。
[root@lhy ~]# ls -i /root/
67145602 anaconda-ks.cfg 101110119 openscap_data
[root@lhy ~]# ls -i .
67145602 anaconda-ks.cfg 101110119 openscap_data
[root@lhy ~]# ls -i .ssh/..
67145602 anaconda-ks.cfg 101110119 openscap_data
[root@lhy ~]# ls -i openscap_data/..
67145602 anaconda-ks.cfg 101110119 openscap_data
[root@lhy ~]# ls -ld /root
dr-xr-x---. 4 root root 184 Jun 1 11:53 /root
[root@lhy ~]# ls -a /root
. anaconda-ks.cfg .bash_logout .bashrc openscap_data .tcshrc
.. .bash_history .bash_profile .cshrc .ssh .viminfo
使用-t选项可以按照时间降序排列。
[root@lhy ~]# ls -lt ..
total 20
drwxrwxrwt. 11 root root 4096 Jun 3 03:10 tmp
drwxr-xr-x. 22 root root 580 Jun 2 23:55 run
drwxr-xr-x. 3 root root 19 Jun 2 23:49 home
drwxr-xr-x. 76 root root 8192 Jun 2 23:49 etc
drwxr-xr-x. 19 root root 3260 Jun 2 23:36 dev
dr-xr-xr-x. 13 root root 0 Jun 2 23:36 sys
dr-xr-xr-x. 178 root root 0 Jun 2 23:36 proc
dr-xr-x---. 4 root root 184 Jun 1 11:53 root
dr-xr-xr-x. 5 root root 4096 May 29 14:21 boot
drwxr-xr-x. 19 root root 267 May 29 14:21 var
drwxr-xr-x. 13 root root 155 May 29 14:01 usr
lrwxrwxrwx. 1 root root 9 May 29 14:01 lib64 -> usr/lib64
lrwxrwxrwx. 1 root root 8 May 29 14:01 sbin -> usr/sbin
lrwxrwxrwx. 1 root root 7 May 29 14:01 lib -> usr/lib
lrwxrwxrwx. 1 root root 7 May 29 14:01 bin -> usr/bin
drwxr-xr-x. 2 root root 6 Nov 5 2016 media
drwxr-xr-x. 2 root root 6 Nov 5 2016 mnt
drwxr-xr-x. 2 root root 6 Nov 5 2016 opt
drwxr-xr-x. 2 root root 6 Nov 5 2016 srv
使用-d选项仅显示目录，不显示其他。
[root@lhy ~]# ls -ld /
dr-xr-xr-x. 17 root root 245 May 31 15:43 /
[root@lhy ~]# ls -lt /
total 20
drwxrwxrwt. 11 root root 4096 Jun 3 03:10 tmp
drwxr-xr-x. 22 root root 580 Jun 2 23:55 run
drwxr-xr-x. 3 root root 19 Jun 2 23:49 home
drwxr-xr-x. 76 root root 8192 Jun 2 23:49 etc
drwxr-xr-x. 19 root root 3260 Jun 2 23:36 dev
dr-xr-xr-x. 13 root root 0 Jun 2 23:36 sys
dr-xr-xr-x. 178 root root 0 Jun 2 23:36 proc
dr-xr-x---. 4 root root 184 Jun 1 11:53 root
dr-xr-xr-x. 5 root root 4096 May 29 14:21 boot
drwxr-xr-x. 19 root root 267 May 29 14:21 var
drwxr-xr-x. 13 root root 155 May 29 14:01 usr
lrwxrwxrwx. 1 root root 9 May 29 14:01 lib64 -> usr/lib64
lrwxrwxrwx. 1 root root 8 May 29 14:01 sbin -> usr/sbin
lrwxrwxrwx. 1 root root 7 May 29 14:01 lib -> usr/lib
lrwxrwxrwx. 1 root root 7 May 29 14:01 bin -> usr/bin
drwxr-xr-x. 2 root root 6 Nov 5 2016 media
drwxr-xr-x. 2 root root 6 Nov 5 2016 mnt
drwxr-xr-x. 2 root root 6 Nov 5 2016 opt
drwxr-xr-x. 2 root root 6 Nov 5 2016 srv
之前也提过，使用man命令可以查看ls的所有参数，我们只需要记住常用的，按需查询即可。
最后，使用别名可以方便输入命令，比如给目录自动添加颜色需要--color=auto的参数，而想只需要ls就能实现，这个会在2.5节讲到。
[root@lhy ~]# which ls
alias ls='ls --color=auto'
/usr/bin/ls
2.4 文件类型
上一小节讲到使用ls -l查看文件的时候第一列显示的是文件的类型与权限。文件类型就是第一个字符表示的。
[root@lhy ~]# ls -la
total 36
dr-xr-x---. 4 root root 184 Jun 1 11:53 .
dr-xr-xr-x. 17 root root 245 May 31 15:43 ..
-rw-------. 1 root root 1622 May 29 14:05 anaconda-ks.cfg
drwxr-xr-x. 2 root root 40 May 29 14:04 openscap_data
drwx------. 2 root root 80 May 31 16:47 .ssh
-rw-------. 1 root root 6877 Jun 1 11:53 .viminfo
d表示这个“文件“是一个目录。’-‘表示这个”文件“是普通文本文档。不管是普通文本文档还是二进制文件，都会显示为’-‘ 。
c表示字符串设备。
[root@lhy ~]# ls -l /dev/tty0
crw--w----. 1 root tty 4, 0 Jun 2 23:36 /dev/tty0
l表示软连接文件，相当于Windows的快捷方式
[root@lhy ~]# ls -l /dev/stderr
lrwxrwxrwx. 1 root root 15 Jun 2 23:36 /dev/stderr -> /proc/self/fd/2
b表示块设备，比如光盘，硬盘等。
[root@lhy ~]# ls -l /dev/sda*
brw-rw----. 1 root disk 8, 0 Jun 2 23:36 /dev/sda
brw-rw----. 1 root disk 8, 1 Jun 2 23:36 /dev/sda1
brw-rw----. 1 root disk 8, 2 Jun 2 23:36 /dev/sda2
brw-rw----. 1 root disk 8, 3 Jun 2 23:36 /dev/sda3
s表示socket文件,用于进程、服务之间通信所用的文件。
[root@lhy ~]# ls -l /dev/log
srw-rw-rw-. 1 root root 0 Jun 2 23:36 log
2.5 alias命令
ls和ll命令其实都是有别名的，我们可以用alias命令查看。
[root@lhy ~]# alias ls
alias ls='ls --color=auto'
[root@lhy ~]# alias ll
alias ll='ls -l --color=auto'
[root@lhy ~]# alias yum
-bash: alias: yum: not found
[root@lhy ~]# alias which
alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
如果存在别名就会显示别名，如果不存在会返回not found。我们发现which的别名中就有alias命令，所以查看一个命令来源可以直接使用which命令。
如果想看所有的有别名命令，直接使用alias即可。
[root@lhy ~]# alias
alias cp='cp -i'
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l.='ls -d .* --color=auto'
alias ll='ls -l --color=auto'
alias ls='ls --color=auto'
alias mv='mv -i'
alias rm='rm -i'
alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
不希望使用别名而想直接应用命令，使用绝对路径即可。
[root@lhy ~]# /bin/ls .
anaconda-ks.cfg openscap_data
下面介绍一个系统的环境变量PATH
[root@lhy ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
可以看到PATH中使用：分割了很多文件目录，只要是在这些目录里的可执行文件都可以直接输入文件名而执行，which查询命令就是在PATH中查询的。
现在，我们创建一个别名aming，比如让它变为ls -lha，使用如下方法
[root@lhy ~]# alias aming='ls -lha'
[root@lhy ~]# aming
total 36K
dr-xr-x---. 4 root root 184 Jun 1 11:53 .
dr-xr-xr-x. 17 root root 245 May 31 15:43 ..
-rw-------. 1 root root 1.6K May 29 14:05 anaconda-ks.cfg
-rw-------. 1 root root 3.2K Jun 1 13:52 .bash_history
-rw-r--r--. 1 root root 18 Dec 29 2013 .bash_logout
-rw-r--r--. 1 root root 176 Dec 29 2013 .bash_profile
-rw-r--r--. 1 root root 176 Dec 29 2013 .bashrc
-rw-r--r--. 1 root root 100 Dec 29 2013 .cshrc
drwxr-xr-x. 2 root root 40 May 29 14:04 openscap_data
drwx------. 2 root root 80 May 31 16:47 .ssh
-rw-r--r--. 1 root root 129 Dec 29 2013 .tcshrc
-rw-------. 1 root root 6.8K Jun 1 11:53 .viminfo
[root@lhy ~]# which aming
alias aming='ls -lha'
/usr/bin/ls
取消别名的方法也很简单，使用unalias + 别名 即可。
[root@lhy ~]# unalias aming
[root@lhy ~]# aming
-bash: aming: command not found
