大家先了解一些背景知識(shí)：

1) 給文件增加了i權(quán)限，那文件不能被更改，不能刪除，也不能修改名字以及權(quán)限。

2) 給文件增加a權(quán)限，文件可以追加內(nèi)容，不能刪除，不能修改內(nèi)容，不能修改名字以及權(quán)限。

3) vim一個(gè)文件，如果不正常退出，再次編輯時(shí)是會(huì)提示一些信息的，并且有一個(gè)隱藏的文件.xxx.swp

了解以上知識(shí)后，再來(lái)看下面的現(xiàn)象：

1) 如果給一個(gè)文件增加a權(quán)限，用vim編輯文件，增加內(nèi)容（注意是在文件末尾增加內(nèi)容，不要修改其他內(nèi)容），并不會(huì)成功。

2) 如果給一個(gè)目錄增加i權(quán)限或者a權(quán)限，在該目錄下面vim一個(gè)文件，更改文件內(nèi)容可以正常保存。

既然a權(quán)限可以追加內(nèi)容，那為何vim一個(gè)文件在末尾增加內(nèi)容不能成功？既然i權(quán)限不能修改，那為何在目錄里面變更文件內(nèi)容卻可以成功？

關(guān)于這兩點(diǎn)，你有沒(méi)有疑惑？下面我們來(lái)分析原因。

先不管i或者a權(quán)限，

在一個(gè)沒(méi)有i或者a權(quán)限的目錄下，編輯一個(gè)沒(méi)有i或者a權(quán)限的文件，

用strace來(lái)查看其執(zhí)行過(guò)程。

mkdir /tmp/test

strace vim /tmp/test/aminglinux.txt 2>/tmp/vim.log

寫(xiě)入一個(gè)數(shù)字1，然后保存退出。再來(lái)查看vim.log的內(nèi)容。

less /tmp/vim.log

大部分內(nèi)容你不用關(guān)心，只需要看這幾行：

stat("/tmp/test/aminglinux.txt", 0x7fff072ecb10) = -1 ENOENT (No such file or directory)

access("/tmp/test/aminglinux.txt", W_OK) = -1 ENOENT (No such file or directory)

open("/tmp/test/aminglinux.txt", O_RDONLY) = -1 ENOENT (No such file or directory)

readlink("/tmp/test/aminglinux.txt", 0x7fff072eb360, 4095) = -1 ENOENT (No such file or directory)

open("/tmp/test/.aminglinux.txt.swp", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/tmp/test/.aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL, 0600) = 3

open("/tmp/test/.aminglinux.txt.swx", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/tmp/test/.aminglinux.txt.swx", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

unlink("/tmp/test/.aminglinux.txt.swx") = 0

unlink("/tmp/test/.aminglinux.txt.swp") = 0

stat("/tmp/test/.aminglinux.txt.swp", 0x7fff072ec310) = -1 ENOENT (No such file or directory)

lstat("/tmp/test/.aminglinux.txt.swp", 0x7fff072ec3e0) = -1 ENOENT (No such file or directory)

lstat("/tmp/test/.aminglinux.txt.swp", 0x7fff072ec8a0) = -1 ENOENT (No such file or directory)

open("/tmp/test/.aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW, 0600) = 3

stat("/tmp/test/aminglinux.txt", 0x7fff072eac40) = -1 ENOENT (No such file or directory)

stat("/tmp/test/aminglinux.txt", 0x7fff072ebe20) = -1 ENOENT (No such file or directory)

stat("/tmp/test/aminglinux.txt", 0x7fff072eadf0) = -1 ENOENT (No such file or directory)

write(1, ""/tmp/test/aminglinux.txt"", 26) = 26

stat("/tmp/test/aminglinux.txt", 0x7fff072ec050) = -1 ENOENT (No such file or directory)

open("/tmp/test/aminglinux.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=2, ...}) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=2, ...}) = 0

unlink("/tmp/test/.aminglinux.txt.swp") = 0

看起來(lái)亂亂的，其實(shí)大概的過(guò)程就是vim /tmp/test/aminglinux.txt時(shí)，先看有沒(méi)有.aminglinux.txt.swp以及.aminglinux.txt.swx，因?yàn)檫@兩個(gè)文件就是vim產(chǎn)生的臨時(shí)文件，swp先產(chǎn)生，如果swp存在就產(chǎn)生第二個(gè)swx。寫(xiě)入的內(nèi)容先存到swp里，當(dāng)保存退出vim時(shí)，再把swp的內(nèi)容存到aminglinux.txt里，最后刪除掉swp文件。

有了這個(gè)認(rèn)識(shí)之后，我們?cè)賮?lái)分析上面提到的現(xiàn)象1。如果文件給了a權(quán)限，那么在編輯該文件時(shí)，會(huì)產(chǎn)生swp文件，當(dāng)保存退出時(shí)，swp文件內(nèi)容會(huì)寫(xiě)入該文件，這相當(dāng)于更改該文件，很線上a權(quán)限是不允許的。

再來(lái)分析現(xiàn)象2，按照我們的推測(cè)，如果目錄給了a權(quán)限，增加文件沒(méi)問(wèn)題，也就是說(shuō)產(chǎn)生swp或者swx文件沒(méi)有問(wèn)題，當(dāng)然把swp或者swx內(nèi)容寫(xiě)入到文件里時(shí)也不會(huì)有問(wèn)題，但swp或者swx文件卻不會(huì)被刪除了，所以再次編輯文件時(shí)就會(huì)提示臨時(shí)文件已經(jīng)存在了。但這并不會(huì)影響修改文件內(nèi)容。

如果給目錄設(shè)置了i權(quán)限的話，vim編輯文件，要產(chǎn)生swp或swx肯定會(huì)出錯(cuò)啊，但為何依然能正常編輯文件？ 下面繼續(xù)用strace來(lái)分析一下。

chattr +i /tmp/test

strace vim /tmp/test/aminglinux.txt 2> /tmp/vim.log

看vim.log里面和aminglinux.txt相關(guān)的信息

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

access("/tmp/test/aminglinux.txt", W_OK) = 0

open("/tmp/test/aminglinux.txt", O_RDONLY) = 3

readlink("/tmp/test/aminglinux.txt", 0x7fff49efc6f0, 4095) = -1 EINVAL (Invalid argument)

open("/tmp/test/.aminglinux.txt.swp", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/tmp/test/.aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EACCES (Permission denied)

stat("/tmp/test/.aminglinux.txt.swp", 0x7fff49efd6a0) = -1 ENOENT (No such file or directory)

lstat("/tmp/test/.aminglinux.txt.swp", 0x7fff49efd770) = -1 ENOENT (No such file or directory)

lstat("/tmp/test/.aminglinux.txt.swp", 0x7fff49efdc30) = -1 ENOENT (No such file or directory)

open("/tmp/test/.aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW, 0600) = -1 EACCES (Permission denied)

readlink("/tmp/test/aminglinux.txt", 0x7fff49efc6f0, 4095) = -1 EINVAL (Invalid argument)

open("/root/tmp/aminglinux.txt.swp", O_RDONLY) = -1 ENOTDIR (Not a directory)

open("/root/tmp/aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 ENOTDIR (Not a directory)

stat("/root/tmp/aminglinux.txt.swp", 0x7fff49efd6a0) = -1 ENOTDIR (Not a directory)

lstat("/root/tmp/aminglinux.txt.swp", 0x7fff49efd770) = -1 ENOTDIR (Not a directory)

lstat("/root/tmp/aminglinux.txt.swp", 0x7fff49efdc30) = -1 ENOTDIR (Not a directory)

open("/root/tmp/aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW, 0600) = -1 ENOTDIR (Not a directory)

readlink("/tmp/test/aminglinux.txt", 0x7fff49efc6f0, 4095) = -1 EINVAL (Invalid argument)

open("/var/tmp/aminglinux.txt.swp", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/var/tmp/aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

open("/var/tmp/aminglinux.txt.swx", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/var/tmp/aminglinux.txt.swx", O_RDWR|O_CREAT|O_EXCL, 0600) = 5

unlink("/var/tmp/aminglinux.txt.swx") = 0

unlink("/var/tmp/aminglinux.txt.swp") = 0

stat("/var/tmp/aminglinux.txt.swp", 0x7fff49efd6a0) = -1 ENOENT (No such file or directory)

lstat("/var/tmp/aminglinux.txt.swp", 0x7fff49efd770) = -1 ENOENT (No such file or directory)

lstat("/var/tmp/aminglinux.txt.swp", 0x7fff49efdc30) = -1 ENOENT (No such file or directory)

open("/var/tmp/aminglinux.txt.swp", O_RDWR|O_CREAT|O_EXCL|O_NOFOLLOW, 0600) = 4

chmod("/var/tmp/aminglinux.txt.swp", 0644) = 0

open("/tmp/test/aminglinux.txt", O_RDONLY) = 3

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

access("/tmp/test/aminglinux.txt", W_OK) = 0

write(1, ""aminglinux.txt"", 16) = 16

stat("aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

access("aminglinux.txt", W_OK) = 0

getxattr("aminglinux.txt", "system.posix_acl_access", 0x7fff49efd050, 132) = -1 ENODATA (No data available)

stat("aminglinux.txt", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0

open("aminglinux.txt", O_WRONLY|O_CREAT|O_TRUNC, 0644) = 3

chmod("aminglinux.txt", 0100644) = 0

setxattr("aminglinux.txt", "system.posix_acl_access", "x02x00x00x00x01x00x06x00xffxffxffxffx04x00x04x00xffxffxffxff x00x04x00xffxffxffxff", 28, 0) = 0

stat("/tmp/test/aminglinux.txt", {st_mode=S_IFREG|0644, st_size=6, ...}) = 0

unlink("/var/tmp/aminglinux.txt.swp") = 0

我相信你可以看到Permission denied的提示，這是因?yàn)楫?dāng)前目錄有i權(quán)限，不能增加文件，也就不能在當(dāng)前目錄下生成臨時(shí)文件。當(dāng)然，vim如果遇到這樣的問(wèn)題，它還是會(huì)“曲線救國(guó)”的，于是先找/root/tmp/，但是并沒(méi)有該目錄，只好繼續(xù)找/var/tmp/，這個(gè)目錄存在，所以就在這個(gè)目錄里生成了臨時(shí)文件（并不是隱藏的）。后面的操作就不用多說(shuō)了。

既然vim可以在/var/tmp/下生成臨時(shí)文件，自然也可以在已經(jīng)設(shè)置了i權(quán)限的目錄里編輯文件的，這樣現(xiàn)象2也解釋通了。上面羅嗦了這么多，其實(shí)我就想表達(dá)如下觀點(diǎn)：

vim編輯文件時(shí)，會(huì)在該文件所在目錄生成臨時(shí)隱藏文件.swp和.swx，如果那目錄不可寫(xiě)就會(huì)到/root/tmp/下或者/var/tmp/下生成臨時(shí)文件（非隱藏），當(dāng)編輯的文件保存后，臨時(shí)文件刪除。