当我尝试在Mac OS X上更新R个软件包时（作为具有管理员权限的普通用户，即/Library/Frameworks/R.framework/Versions/3.0/Resources对我来说可写），我明白了：
> update.packages(instlib = .libPaths()[1], checkBuilt=TRUE, ask=FALSE)
Warning: package 'foreign' in library '/Library/Frameworks/R.framework/Versions/3.0/Resources/library' will not be updated
Warning: package 'lattice' in library '/Library/Frameworks/R.framework/Versions/3.0/Resources/library' will not be updated
Warning: package 'Matrix' in library '/Library/Frameworks/R.framework/Versions/3.0/Resources/library' will not be updated
Warning: package 'mgcv' in library '/Library/Frameworks/R.framework/Versions/3.0/Resources/library' will not be updated
Warning: package 'plotrix' in library '/Library/Frameworks/R.framework/Versions/3.0/Resources/library' will not be updated
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/contrib/3.0/Hmisc_3.13-0.tgz'
Content type 'application/x-gzip' length 1514975 bytes (1.4 Mb)
opened URL
==============================================
downloaded 1.3 Mb
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/contrib/3.0/Matrix_1.1-1.1.tgz'
Content type 'application/x-gzip' length 3450203 bytes (3.3 Mb)
opened URL
==================================================
downloaded 3.3 Mb
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/contrib/3.0/nleqslv_2.1.tgz'
Content type 'application/x-gzip' length 89297 bytes (87 Kb)
opened URL
==================================================
downloaded 87 Kb
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/contrib/3.0/plotrix_3.5-2.tgz'
Content type 'application/x-gzip' length 624295 bytes (609 Kb)
opened URL
========
downloaded 108 Kb
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/contrib/3.0/nlme_3.1-113.tgz'
Content type 'application/x-gzip' length 2132159 bytes (2.0 Mb)
opened URL
==========
downloaded 457 Kb
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/contrib/3.0/rpart_4.1-4.tgz'
Content type 'application/x-gzip' length 890223 bytes (869 Kb)
opened URL
==================================================
downloaded 869 Kb
Hmisc/help/Hmisc.rdb: (Empty error message)
tar: Error exit delayed from previous errors.
plotrix/R/plotrix.rdb: (Empty error message)
tar: Error exit delayed from previous errors.
Error: file ‘/var/tmp/RtmpY8MhsZ/downloaded_packages/plotrix_3.5-2.tgz’ is not an OS X binary package
In addition: Warning messages:
1: In download.file(url, destfile, method, mode = "wb", ...) :
downloaded length 1402861 != reported length 1514975
Calls: update.packages -> install.packages -> .install.macbinary -> download.packages -> try -> tryCatch -> tryCatchList -> tryCatchOne -> doTryCatch -> download.file
2: In download.file(url, destfile, method, mode = "wb", ...) :
downloaded length 111247 != reported length 624295
Calls: update.packages -> install.packages -> .install.macbinary -> download.packages -> try -> tryCatch -> tryCatchList -> tryCatchOne -> doTryCatch -> download.file
3: In download.file(url, destfile, method, mode = "wb", ...) :
downloaded length 468901 != reported length 2132159
Calls: update.packages -> install.packages -> .install.macbinary -> download.packages -> try -> tryCatch -> tryCatchList -> tryCatchOne -> doTryCatch -> download.file
4: 'tar' returned non-zero exit code 1
5: 'tar' returned non-zero exit code 1
Execution halted
.tgz中的/var/tmp/RtmpY8MhsZ/downloaded_packages/个文件是有效的tar / gzip文件：
$ tar tvfz /var/tmp/RtmpY8MhsZ/downloaded_packages/Matrix_1.1-1.1.tgz
drwxrwxr-x 0 root admin 0 Jan 1 01:47 Matrix/
-rw-rw-r-- 0 root admin 2433 Jan 1 01:45 Matrix/Copyrights
drwxrwxr-x 0 root admin 0 Jan 1 01:45 Matrix/data/
-rw-rw-r-- 0 root admin 1253 Jan 1 01:45 Matrix/DESCRIPTION
drwxrwxr-x 0 root admin 0 Jan 1 01:47 Matrix/doc/
-rw-rw-r-- 0 root admin 72521 Jan 1 01:45 Matrix/Doxyfile
drwxrwxr-x 0 root admin 0 Jan 1 01:45 Matrix/external/
drwxrwxr-x 0 root admin 0 Jan 1 01:47 Matrix/help/
drwxrwxr-x 0 root admin 0 Jan 1 01:47 Matrix/html/
drwxrwxr-x 0 root admin 0 Jan 1 01:45 Matrix/include/
.....