What are some reasons an installed package won't be found by a call to loadNamespace() ?
tl;dr The installing processx cannot find ps package, even though ps package is installed.
Install ps package
I'm Installing processx as a dependency to roxygen2. Installing processx failed claiming package ps was not found. To remedy, installed ps manually.
installing via 'install.libs.R' to /home/grosscol/R/x86_64-pc-linux-gnu-library/3.5/ps
** byte-compile and prepare package for lazy loading
*** installing help indices
** building package indices
** testing if installed package can be loaded
- DONE (ps)
## Check ps package installation Restart the R session, and check. Installation of ps appears to have worked. ```r > packageVersion("ps") #  ‘1.1.0’ ps::ps_boot_time() #  "2018-10-15 12:50:17 GMT"
Error installing processx package persists
Go to retry processx installation, and it fails again with the same error message.
installing via 'install.libs.R' to /home/grosscol/R/x86_64-pc-linux-gnu-library/3.5/processx ** R ** inst ** byte-compile and prepare package for lazy loading ** help *** installing help indices ** building package indices ** testing if installed package can be loaded Error: package or namespace load failed for ‘processx’: .onLoad failed in loadNamespace() for 'processx', details: call: loadNamespace(name) error: there is no package called ‘ps’ Error: loading failed Execution halted ERROR: loading failed * removing ‘/home/grosscol/R/x86_64-pc-linux-gnu-library/3.5/processx’ Warning in install.packages : installation of package ‘processx’ had non-zero exit status
Where to check for problems?
I don't know where else to look for the source of this problem as .libPaths() appears to be correct.
> .libPaths() #  "/home/grosscol/R/x86_64-pc-linux-gnu-library/3.5" "/usr/local/lib/R/site-library" #  "/usr/lib/R/site-library" "/usr/lib/R/librar
Any suggestions for a different angle to poke at this? Or another location to check in an R-3.5.1 installation on Ubuntu bionic (x86_64-pc-linux-gnu)?